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/image-configuration.yaml

@@ -105,7 +105,11 @@ tests:
   - it: correctly renders floating tag references
     template: templates/gitea/deployment.yaml
     set:
-      deployment.gitea.image.tag: 1.21 # use non-quoted value on purpose. See: https://gitea.com/gitea/helm-gitea/issues/631
+      # use non-quoted values on purpose. See: https://gitea.com/gitea/helm-gitea/issues/631
+      deployment.gitea.image.tag: 1.21
+      deployment.initDirectories.image.tag: 1.21
+      deployment.initAppIni.image.tag: 1.21
+      deployment.initConfigureGitea.image.tag: 1.21
     asserts:
       - equal:
           path: spec.template.spec.initContainers[0].image
@@ -119,3 +123,18 @@ tests:
       - equal:
           path: spec.template.spec.containers[0].image
           value: "docker.gitea.com/gitea:1.21-rootless"
+  - it: init containers use their own image configuration
+    template: templates/gitea/deployment.yaml
+    set:
+      deployment.initDirectories.image.registry: "init.example.com"
+      deployment.initDirectories.image.tag: "1.19.4"
+    asserts:
+      - equal:
+          path: spec.template.spec.initContainers[0].image
+          value: "init.example.com/gitea:1.19.4-rootless"
+      - equal:
+          path: spec.template.spec.initContainers[1].image
+          value: "docker.gitea.com/gitea:1.19.3-rootless"
+      - equal:
+          path: spec.template.spec.containers[0].image
+          value: "docker.gitea.com/gitea:1.19.3-rootless"