Expand ${...} image tags using availableVersions

[ArnobKumarSaha]

Problem

kubestash addon Function resources (rendered by the kubedb-kubestash-catalog chart) carry an image whose tag has a ${DB_VERSION}-style placeholder alongside a sibling availableVersions list:

spec:
  availableVersions: ["16.4", "17.2", "18.2"]
  image: ghcr.io/kubedb/postgres-restic-plugin:v0.29.0_${DB_VERSION}

lib.collectImages stored the raw templated string, and ListImages/GroupImages drop anything containing ${. As a result these plugin images silently never made it into imagelist.yaml.

Change

• collectImages now runs each image value through expandVersionedImage, which substitutes a ${...} placeholder with every entry in the object's availableVersions list, emitting one concrete image per version.
• No placeholder, or no usable availableVersions → returned unchanged, so the existing ${ filter still drops any genuinely unresolvable templated image (no regression).

For the example above, list now emits:

ghcr.io/kubedb/postgres-restic-plugin:v0.29.0_16.4
ghcr.io/kubedb/postgres-restic-plugin:v0.29.0_17.2
ghcr.io/kubedb/postgres-restic-plugin:v0.29.0_18.2

ace_up.go's separate collectImages is left untouched — that flow only reads PostgresVersion/RedisVersion from the kubedb-catalog chart, never these kubestash Function resources.

Test

Added pkg/lib/image_test.go covering the Function shape and the helper's edge cases. go build ./... and the new tests pass.