Allow skip_ci to be passed to rebase

Related issue: #38141 (closed)

What does this MR do?

• Allow skip_ci parameter to be accepted via Merge Request rebase API endpoint
• Send skip_ci flag all the way down to to Gitaly Rebase RPC call
• In Gitaly (gitaly!1748 (merged)) the new parameter is converted to push options and sent back to Rails
• Rails will use it as push options in the PostReceive hook to skip CI.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability 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