Add reusable container-login composite action for Forgejo registry

.forgejo/actions/container-login/action.yml

@@ -0,0 +1,21 @@
+name: "Forgejo Container Registry Login"
+description: "Logs into the Forgejo container registry"
+inputs:
+  registry:
+    description: "Container registry hostname"
+    required: false
+    default: "git.mcintire.me"
+  username:
+    description: "Registry username"
+    required: false
+    default: "graham"
+  token:
+    description: "Forgejo access token with packages:read + packages:write scopes"
+    required: true
+
+runs:
+  using: "composite"
+  steps:
+    - name: Login to Forgejo Container Registry
+      shell: bash
+      run: echo "${{ inputs.token }}" | docker login ${{ inputs.registry }} -u ${{ inputs.username }} --password-stdin