fix(deployment): run plugin container as the reposilite user

The reposilite entrypoint chowns /app to 977:977 whenever it starts as root. The plugin container downloaded
the jar as its own image user (101), so after the first start the file was owned by 977:977 with mode 0644.
Since the plugins emptyDir survives a container restart within the same pod, a restarted plugin container
could no longer overwrite the existing jar and aborted with "Permission denied", which left the pod in a
permanent Init:CrashLoopBackOff until the pod itself was recreated.

Run the plugin container as 977:977 by default and expose the security context as
deployment.pluginContainer.securityContext, so it can be aligned when PUID/PGID are overridden.

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

values.yaml

@@ -178,6 +178,15 @@ deployment:
       tag: "8.22.0"
       pullPolicy: IfNotPresent
 
+    ## @param deployment.pluginContainer.securityContext.runAsGroup Group id of the plugin container.
+    ## @param deployment.pluginContainer.securityContext.runAsUser User id of the plugin container.
+    # Reposilite chowns /app to 977:977 when its entrypoint starts as root. Downloading the plugin as a
+    # different user leaves behind a file the plugin container can no longer overwrite, which breaks every
+    # restart that reuses the emptyDir. Align this with PUID/PGID when those are overridden.
+    securityContext:
+      runAsGroup: 977
+      runAsUser: 977
+
   ## @param deployment.priorityClassName PriorityClassName of the Reposilite deployment.
   priorityClassName: ""