feat: Add MergeTrain options

[BigGold1310]

Description of your changes

Add support for MergeTrainsEnabled, MergeTrainsSkipTrainAllowed, and MergePipelinesEnabled fields to the GitLab Project resource.

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

[henrysachs]

@BigGold1310 is this ready for review?

[henrysachs]

@BigGold1310 I would love to merge this, is this fine for you?

[BigGold1310]

@henrysachs Ready for review.

[henrysachs]

Thanks for the PR @BigGold1310 — this looks very close.

I may be missing something, but I think there are still two controller-side gaps:

1. isProjectUpToDate() in pkg/namespaced/controller/projects/projects/project.go (and the generated mirror in pkg/cluster/controller/projects/projects/zz_project.go) still does not compare mergeTrainsEnabled, mergeTrainsSkipTrainAllowed, or mergePipelinesEnabled.
   That means a spec change limited to these fields would still be treated as up to date, so EditProject would never be called for that change.

2. lateInitialize() in the same controller files does not seem to backfill these new fields into spec.forProvider when they are unset.
   So adopted/imported resources, or projects relying on GitLab defaults, would not get these values initialized the same way as nearby optional project settings.

The API / CRD / client wiring looks good to me — it just seems the reconcile path is not fully wired for the new fields yet.