Have and use a repo shared between core developers for storing test suite secrets

Now that we have solved #6301 (closed) and #8188 (closed), one can add any secrets they want to features/config/local.yml. However, this doesn’t solve the following use cases yet:

• our automatic build robots will need to be fed with the secrets they need
• core developers may want to share a set of secrets, for ease of maintenance and test reproducibility

Ideas and possible requirements:

• Something that supports a “—additional-config-directory DIR” option would be nice, so that one can point it to the checkout of the secrets repo. E.g. command-line > features/config/local.yml > ADDITIONAL_CONFIG_DIR/*.yml > features/config/defaults.yml.
• features/config/local.d/*.yml but then people need to create symlinks from there to the checkout of the secrets repo.

Subtasks

• #9220 (closed)
• #9221 (closed)
• #9222 (closed)

Related issues

• Related to #6301 (closed)
• Related to #9142 (closed)
• Blocks #6304 (closed)

Original created by @intrigeri on 8920 (Redmine)