feat(autolabels): Add the "autolabels" job.

Issue: gitlab-com/gl-infra/common-ci-tasks#34

autolabels.yml

+spec:
+  inputs:
+    stage:
+      default: "build"
+    version:
+      default: "v${GL_AUTOLABELS_VERSION}"
+    vault:
+      default: ""
+---
+
+# Include exactly one of the following files:
+include:
+  # Option 1: Vault with explicit path from the "vault" input
+  - local: 'internal/autolabels/vault.yml'
+    rules:
+      - if: '"$[[ inputs.vault | expand_vars ]]" != ""'
+    inputs:
+      vault: "$[[ inputs.vault | expand_vars ]]"
+  # Option 2: Variable using AUTOLABELS_TOKEN (compatibility behavior)
+  - local: 'internal/autolabels/variable.yml'
+    rules:
+      - if: '"$[[ inputs.vault | expand_vars ]]" == "" && $AUTOLABELS_TOKEN != null'
+  # Option 3 (default): Vault using a well-known default path
+  - local: 'internal/autolabels/vault.yml'
+    rules:
+      - if: '"$[[ inputs.vault | expand_vars ]]" == "" && $AUTOLABELS_TOKEN == null'
+    inputs:
+      vault: "access_tokens/${VAULT_SECRETS_PATH}/autolabels/token@ci"
+
+  # Include the "autolabels 🏷️" job from the autolabels repository.
+  - project: 'gitlab-com/gl-infra/autolabels'
+    ref: v1.2.3  # renovate:managed
+    file: 'ci-tasks/autolabels.yml'
+    inputs:
+      stage: $[[ inputs.stage ]]
+
+# Amend the "extends" field to the "autolabels 🏷️" job.
+autolabels 🏷️:
+  extends: .autolabels_auth  # Vault or CI variable, from internal/autolabels/{vault,variable}.yml

internal/autolabels/variable.yml

+# DO NOT INCLUDE DIRECTLY!
+---
+.autolabels_auth:
+  variables:
+    AUTOLABELS_AUTH_SOURCE: "CI/CD Variables"

internal/autolabels/vault.yml

+# DO NOT INCLUDE DIRECTLY!
+spec:
+  inputs:
+    vault:
+--- 
+.autolabels_auth:
+  id_tokens:
+    VAULT_ID_TOKEN:
+      aud: https://vault.gitlab.net
+  variables:
+    AUTOLABELS_AUTH_SOURCE: "Vault"
+  secrets:
+    AUTOLABELS_TOKEN:
+      file: false
+      vault: $[[ inputs.vault ]]
+      token: $VAULT_ID_TOKEN