[GEOT-7563] Allow to recompute an image mosaic summary Raster Attribute Table

[aaime]

Useful if new files are added or existing files are updated, that contain a different set of RAT entries (not done automatically, it can be expensive and the RAT might be uniform across files).

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).
• Avoid Java 9+ split packages.
• 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).
• There is an issue in GeoTools Jira (except for changes not visible to end users).
• Commit message(s) must be in the form [GEOT-XYZW] Title of the Jira ticket.
• Bug fixes and small new features are presented as a single commit.
• The commit targets a single objective (if multiple focuses cannot be avoided, each one is in its own commit, and has a separate ticket describing it).

[dromagnoli]

Looks good to me. I think there is only a small typo on a comment describing what the test is doing.

[dromagnoli]

is it "not add" or is it actually "now add" ?

[aaime]

Yep