WIP: Replace redis language with primary secondary

What does this MR do?

Large parts of the Redis code refer to a primary and secondary setup as master/slave. This language is not consistent with other parts of the product where we use primary/secondary. In my view, this change aligns with our values and should be modified where possible.

This may necessitate renaming some fields in gitlab.rb as well, but this needs to be handled in a separate MR for the Omnibus project

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team