[GEOS-11376] Graduate Raster Attribute Table to extension

[aaime]

See https://github.com/geoserver/geoserver/wiki/GSIP-222

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).
• All the build checks are green (see automated QA checks).

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).

[aaime]

The backport to 2.25.x failed:

The process '/usr/bin/git' failed with exit code 1

stderr

error: could not apply 734a61908d... [GEOS-11376] Graduate Raster Attribute Table to extension
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".

stdout

Auto-merging src/community/pom.xml
Auto-merging src/community/release/pom.xml
Auto-merging src/extension/pom.xml
Auto-merging src/extension/rat/pom.xml
CONFLICT (content): Merge conflict in src/extension/rat/pom.xml
Auto-merging src/pom.xml
Auto-merging src/release/pom.xml
Auto-merging src/web/app/pom.xml

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.25.x 2.25.x
# Navigate to the new working tree
cd .worktrees/backport-2.25.x
# Create a new branch
git switch --create backport-7581-to-2.25.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 734a61908d9ac0c59c8c43e63001873fc9c62bb1
# Push it to GitHub
git push --set-upstream origin backport-7581-to-2.25.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.25.x

Then, create a pull request where the base branch is 2.25.x and the compare/head branch is backport-7581-to-2.25.x.