Docs: Basic documentation for Secrets Manager, linked from UI

Why we are doing this?

We need to update our documentation with basic instructions on how to use the Secrets Manager.

Help links should be updated in the UI so they link to the documentation.

This is for users joining the closed experiment, and later on the closed Beta.

Note: We're introducing a new doc page that is NOT referenced in doc navigation.

Implementation plan

• Add new doc page w/ basic instructions. The page is NOT referenced.
  • How to enable the feature.
  • How to manage secrets.
  • How to manage permissions. #470663 (comment 2658613322)
  • How to use the feature in CI/CD jobs, similar to https://docs.gitlab.com/ci/secrets/#use-vault-secrets-in-a-ci-job.
• Add Learn more to the following pages, and link to the new documentation page:
  • Permissions settings (Settings > General > Visibility, project features, permissions)
  • Secrets manager empty state #470663 (comment 2658613322)
  • Secrets manager index page (table)

Who can address the issue

grouppipeline security engineers implementing this feature.

Other links/references

Documentation Links:

• Pipeline Security entry page
• CI/CD Variables
• External Secrets (Vault by HashiCorp, Google Cloud Secret Manager, Azure Key Vault)
• CI/CD YAML syntax reference

Docs: Add GitLab Secrets Manager to user docs (#550380) covers the additional documentation on introducing the Secrets Manager to our users, and helping them differentiate it from other features we currently provide.