Refactor extension assembly to per-module descriptors

Refactors the extension assembly build system to match the pattern used by community modules, where each extension manages its own assembly descriptor instead of having centralized descriptors in src/release/ext-*.xml.

Motivation

• Improves maintainability by keeping assembly configuration with the module code
• Makes extensions self-contained and easier to understand
• Follows the same pattern as community modules for consistency
• Allows independent management of packaging requirements per extension
• Simplifies adding new extensions - no need to modify central files

Changes

Per-Module Assembly Descriptors

• Removed 52 centralized assembly descriptors from src/release/ext-*.xml
• Removed assembly descriptor references from src/pom.xml maven-assembly-plugin configuration
• Created 52 per-module assembly descriptors at src/assembly/assembly.xml
• Created dedicated -assembly coordinator modules for multi-module extensions:
  • csw-assembly, csw-iso-assembly, dxf-assembly
  • excel-wfs-assembly, excel-wps-assembly
  • importer-assembly, ogcapi-features-assembly
  • wps-assembly, wps-cluster-hazelcast-assembly
• Created pseudo-modules for GeoTools-only extensions (iau, pyramid)

Assembly Profile

Added assembly profile to src/extension/pom.xml:

• maven-antrun-plugin: Checks for src/assembly/assembly.xml existence, skips if not present
• maven-dependency-plugin: Copies module dependencies to target/dependency/
• maven-assembly-plugin: Creates ZIP packages using per-module descriptors
• Output location: src/target/release/ (same as before for compatibility with release scripts)

Assembly Descriptor Structure

Each assembly descriptor includes:

• Module JAR from target/ directory (via first fileSet)
• Dependencies from target/dependency/ (via second fileSet)
• License files from ${geoserverBaseDir}/release/target/html/licenses
• README and LICENSE files (markdown and HTML versions)

dependencySets Migration Support

Implemented infrastructure for future migration to <dependencySets> approach:

• Added assembly.useDependencySets property check in assembly profiles
• When set to true, maven-dependency-plugin skips copying dependencies
• Saves ~7GB disk space (extensions) and ~9GB (community) when used
• Available in both src/extension/pom.xml and src/community/pom.xml
• Reference implementation: gwc-gcs-blob community module
• Migration guide documented in src/extension/README.md

Documentation

• Created src/extension/README.md with:
  • Build instructions (2-step process)
  • Assembly configuration explanation
  • Extension types (single-module, multi-module, pseudo-modules)
  • Assembly descriptor structure and conventions
  • dependencySets migration guide for future optimization
  • Instructions for adding new extensions
• Updated src/release/README.md with new build process
• Updated doc/en/developer/source/policies/community-modules.rst:
  • Changed reference from src/release/ext-h2.xml to src/extension/h2/src/assembly/assembly.xml
  • Updated instructions for adding new extensions

Build Instructions

Building extensions now requires 2 steps:

cd src
# Step 1: Build and install all modules to local Maven repo
mvn clean install -Prelease -DskipTests

# Step 2: Package extensions into ZIP files (NO clean)
cd extension
mvn install -Prelease,assembly -DskipTests

Important: Do NOT use clean in step 2 - it would wipe out compiled classes needed for assembly.

Extension ZIP files are created in src/target/release/ (same location as before).

Status

• All 52 extension assemblies have per-module descriptors
• Assembly descriptors follow consistent pattern with two fileSets (target/ and target/dependency/)
• Output location remains src/target/release/ for compatibility with existing release scripts
• Verification pending: Need to build all extensions and compare against main branch artifacts to ensure identical ZIPs

Future Improvements

Extensions can gradually migrate to <dependencySets> approach for:

• Significant disk space savings: ~7GB (extensions) + ~9GB (community) = ~16GB total
• Faster builds: No dependency copying step
• Simpler descriptors: ~20 lines vs ~40-50 lines per assembly.xml
• Auto-correct dependencies: Resolved directly from pom.xml, no manual JAR patterns

See src/extension/README.md for migration guide and example.

Assembly Descriptor Migration Map

The following table shows where each centralized assembly descriptor was relocated:

Note: The following centralized descriptors from main branch are not in the extension module (may be in community or removed):

• src/release/ext-authbasic.xml
• src/release/ext-geofence-server-h2.xml
• src/release/ext-geofence-server-postgres.xml
• src/release/ext-geofence-wps.xml

Checklist

• I have read the contribution guidelines.
• I have sent a Contribution Licence Agreement (not required for small changes, e.g., fixing typos in documentation).
• First PR targets the main branch (backports managed later; ignore for branch specific issues).

For core and extension modules:

• New unit tests have been added covering the changes.
• Documentation has been updated (if change is visible to end users).
• The REST API docs have been updated (when changing configuration objects or the REST controllers).
• There is an issue in the GeoServer Jira (except for changes that do not affect administrators or end users in any way).
• Commit message(s) must be in the form [GEOS-XYZWV] Title of the Jira ticket.
• Bug fixes and small new features are presented as a single commit.
• Each commit has a single objective (if there are multiple commits, each has a separate JIRA ticket describing its goal).

The PR will be merged when all the build checks are green (see automated QA checks), there is a code committer review, and the checklist has been fulfilled.