feat(manager/dockerfile): support file names that are all lowercase

docs/usage/configuration-options.md

@@ -932,7 +932,7 @@ At other times, the possible files is too vague for Renovate to have any default
 For default, Kubernetes manifests can exist in any `*.yaml` file and we don't want Renovate to parse every single YAML file in every repository just in case some of them have a Kubernetes manifest, so Renovate's default `fileMatch` for manager `kubernetes` is actually empty (`[]`) and needs the user to tell Renovate what directories/files to look in.
 
 Finally, there are cases where Renovate's default `fileMatch` is good, but you may be using file patterns that a bot couldn't possibly guess about.
-For example, Renovate's default `fileMatch` for `Dockerfile` is `['(^|/|\\.)Dockerfile$', '(^|/)Dockerfile[^/]*$']`.
+For example, Renovate's default `fileMatch` for `Dockerfile` is `['(^|/|\\.)([Dd]ocker|[Cc]ontainer)file$', '(^|/)([Dd]ocker|[Cc]ontainer)file[^/]*$']`.
 This will catch files like `backend/Dockerfile`, `prefix.Dockerfile` or `Dockerfile-suffix`, but it will miss files like `ACTUALLY_A_DOCKERFILE.template`.
 Because `fileMatch` is mergeable, you don't need to duplicate the defaults and could just add the missing file like this:
 

lib/modules/manager/dockerfile/index.ts

@@ -8,8 +8,8 @@ export { extractPackageFile };
 
 export const defaultConfig = {
   fileMatch: [
-    '(^|/|\\.)(Docker|Container)file$',
-    '(^|/)(Docker|Container)file[^/]*$',
+    '(^|/|\\.)([Dd]ocker|[Cc]ontainer)file$',
+    '(^|/)([Dd]ocker|[Cc]ontainer)file[^/]*$',
   ],
 };