feat(deployment)!: configurable init containers and Secret checksum lookup

The chart-managed init containers were hardcoded inside `deployment.yaml`. Their image, environment, resources,
security context and volume mounts could not be adjusted individually, and custom init containers could only be
prepended or appended as a whole via `preExtraInitContainers`/`postExtraInitContainers`.

The init containers are now rendered from `deployment.initContainers`, an ordered list whose entries either `link` a
chart-managed init container (`initDirectories`, `initAppIni`, `initConfigureGPG`, `initConfigureGitea`) or provide a
free-form `container` definition. This allows custom containers at any position and makes the execution order
explicit. Each linked init container has its own configuration block in `values.yaml` and falls back to
`deployment.gitea.securityContext` and `initContainers.resources` when unset.

To support per-container images, `gitea.image` was split into the generic helper `gitea.image.name`, which renders an
arbitrary `image` dict instead of only `deployment.gitea.image`.

The pod annotations moved from `deployment.yaml` into the new helper `gitea.pod.annotations`. The SHA sum annotations
now also cover user-provided Secrets: their content is unknown to the chart, so the Secret is read from the cluster via
Helm's `lookup` function. Chart-managed Secrets keep using the rendered manifest, because the cluster still holds their
pre-upgrade state during rendering.

Because `lookup` requires `get` permission on Secrets and silently returns nothing during client-side rendering
(`helm template`, `--dry-run`, Argo CD without a live cluster), `addSHASumAnnotation` now defaults to `false`. The
trade-offs are documented in the README so users can make an informed decision.

BREAKING CHANGE: `preExtraInitContainers` and `postExtraInitContainers` have been removed. Add an entry with a
`container` key before or after the linked init containers in `deployment.initContainers` instead.

BREAKING CHANGE: `secrets.<secret>.addSHASumAnnotation` now defaults to `false`. Set it to `true` explicitly to keep
the rollout trigger on Secret changes.

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

unittests/helm/deployment/deprecations.yaml

@@ -83,6 +83,22 @@ tests:
     asserts:
       - failedTemplate:
           errorMessage: "`podSecurityContext` does no longer exist. Please refer to the changelog and configure `deployment.securityContext` instead."
+  - it: fails when the removed `postExtraInitContainers` value is set
+    set:
+      postExtraInitContainers:
+        - name: post-init-container
+          image: docker.io/library/busybox
+    asserts:
+      - failedTemplate:
+          errorMessage: "`postExtraInitContainers` does no longer exist. Please refer to the changelog and append an entry with a `container` key to `deployment.initContainers` instead."
+  - it: fails when the removed `preExtraInitContainers` value is set
+    set:
+      preExtraInitContainers:
+        - name: pre-init-container
+          image: docker.io/library/busybox
+    asserts:
+      - failedTemplate:
+          errorMessage: "`preExtraInitContainers` does no longer exist. Please refer to the changelog and prepend an entry with a `container` key to `deployment.initContainers` instead."
   - it: fails when the removed `resources` value is set
     set:
       resources:
@@ -158,6 +174,12 @@ tests:
         foo: bar
       podSecurityContext:
         fsGroup: 1000
+      postExtraInitContainers:
+        - name: post-init-container
+          image: docker.io/library/busybox
+      preExtraInitContainers:
+        - name: pre-init-container
+          image: docker.io/library/busybox
       priorityClassName: high-priority
       replicaCount: 2
       resources: