Move secrets feature docs metadata to pipeline authoring

doc/ci/examples/authenticating-with-hashicorp-vault/index.md

 ---
-stage: Release
-group: Release
+stage: Verify
+group: Pipeline Authoring
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 type: tutorial
 ---

doc/ci/secrets/index.md

 ---
-stage: Configure
-group: Configure
+stage: Verify
+group: Pipeline Authoring
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 type: concepts, howto
 ---