self-validate: allow to define config file as an input

.github/workflows/renovate-validate.yaml

@@ -1,5 +1,13 @@
 name: Validate renovate config
-on: workflow_call
+on:
+  workflow_call:
+    inputs:
+      config:
+        required: false
+        type: string
+        default: ""
+        description: |-
+          Space-separated list of configs to validate. If empty (recommended), renovate find the config for you.
 
 jobs:
   validate:
@@ -12,4 +20,17 @@ jobs:
         run: |
           # Renovate updates the line below. Please keep its formatting as it is.
           RENOVATE_IMAGE=ghcr.io/renovatebot/renovate:39.17.0@sha256:89ad65038d8898af0f9deb09aec3377396d603e19a4573a844e70c23ddafd954
-          docker run -i --rm -v "$(realpath .):/repo" -w /repo --entrypoint renovate-config-validator "$RENOVATE_IMAGE" --strict
+          if [[ -z "${{ inputs.config }}" ]]; then
+            docker run -i --rm -v "$(realpath .):/repo" -w /repo --entrypoint renovate-config-validator "$RENOVATE_IMAGE" --strict
+            exit 0
+          fi
+
+          success="true"
+          for c in "${{ inputs.config }}"; do
+            if ! docker run -i --rm -v "$(realpath .):/repo" -w /repo --entrypoint renovate-config-validator "$RENOVATE_IMAGE" --strict "$c"; then
+              echo "::error file=$c,title=Validation failed::Config file did not pass validation"
+              success="false"
+            fi
+          done
+
+          [[ "$success" = "true" ]]