feat(deployment)!: move image to deployment.gitea.image

The `image` values only ever configured the Gitea container itself — registry, repository, tag, digest,
pull policy and the rootless variant are all consumed by the `gitea` container and its init containers.
Keeping them at the top level suggested a chart-wide scope that never existed and separated them from the
other container-scoped settings that already live under `deployment.gitea` (`env`, `resources`).
Moving the block makes the container configuration self-contained and continues the consolidation of all
pod- and Deployment-scoped values under the `deployment` dict.

`imagePullSecrets` intentionally stays top-level, because it is a pod-level setting that also applies to
`extraContainers` and is paired with `global.imagePullSecrets`.

BREAKING CHANGE: `image` no longer exists. Use `deployment.gitea.image` instead. Values still set under
`image` are silently ignored, which would drop a pinned `tag` or `digest` and roll out the chart default
(`appVersion`) instead — review your values before upgrading.

Co-authored-by: Copilot <copilot@github.com>

unittests/helm/init/init_directory_structure.sh-rootless.yaml

@@ -65,7 +65,7 @@ tests:
   - it: it does not chown /data even when image.fullOverride is set
     template: templates/gitea/secret_init.yaml
     set:
-      image.fullOverride: docker.gitea.com/gitea:1.20.5
+      deployment.gitea.image.fullOverride: docker.gitea.com/gitea:1.20.5
     asserts:
       - equal:
           path: stringData["init_directory_structure.sh"]