Hide resolve conflicts button on source branch protected

What does this MR do?

This MR hides "Resolve conflicts button" in case when it was originally disabled (due to protected source branch). The popover informing about "Resolve conflicts" feature is removed. The popover was not showing up due to bug, anyway.

I would like this MR to be a part of my GitLab Hackathon participation. cc/ @cbacharakis .

Screenshots (strongly suggested)

The popover removed by this MR and "Resolve conflicts" button that this MR hides on condition:

After change, "Resolve conflicts" button not visible (source branch protected):

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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

Related to #296888 (closed)