feat(get-images-from-files): add support for helm values (#29)

Adding support for images inside of helm value files as per helm convention.
Limitation: Default images the chart may propose are not exposed and therefore not supported, only what's specifically mentioned in the values file.

Reviewed-on: t.behrendt/trivy-actions#29
Reviewed-by: branch-buddy <branch-buddy@t00n.de>
Co-authored-by: t.behrendt <t.behrendt@t00n.de>
Co-committed-by: t.behrendt <t.behrendt@t00n.de>

get-images-from-files/README.md

@@ -1,11 +1,20 @@
 # Get Images From Files Action
 
-A reusable Gitea Action, that extracts docker images from selected files in a repository.
-
-The action supports Dockerfiles, Kubernetes manifests, and Docker Compose/compose files. Other files are supported if they have a recognizable image reference. Duplicate image references are deduplicated.
+A reusable Gitea Action that extracts Docker image references from selected files in a repository. Duplicate refs are deduplicated.
 
 **Note:** Only fully-qualified refs (with registry, e.g. `docker.io/library/alpine:latest`, `gcr.io/distroless/static:nonroot@sha256:...`) are included; short refs like `alpine:latest` are omitted as their use is discouraged.
 
+## Supported file formats
+
+| Format | How images are extracted |
+| ------ | ------------------------- |
+| **Dockerfile** | `FROM` lines; the image ref is the last token (handles `FROM --platform=... <image>`). |
+| **Kubernetes manifests** | Lines with `image:` (e.g. under `containers` / `initContainers`); the value is taken as the image ref. |
+| **Docker Compose / Compose** | Same as Kubernetes: `image:` key under services. |
+| **Helmfile values** | Pairs of `repository` and `tag` (both required) at the same indent; ref is `repository:tag`. A lone `tag` without `repository` is skipped. |
+
+Other files are supported if they use one of these patterns (e.g. `image:` or `FROM`).
+
 ## Usage
 
 ### Basic Usage