Emit Bitbucket Server Importer metrics

What does this MR do?

This MR:

• Adds Bitbucket Server metrics emission, similar to Bitbucket Importer added here !27524 (merged)
• Removes recently added Gitlab::Import::Metrics. Unfortunately this meta solution did not work well when used in more than 1 importer, that needed to cover 2 methods with the same name (e.g. execute). This is something I missed in the original implementation. Because we defined a method if a prepended module, methods with the same name got redefined, instead of having two separate implementations
• For this reason, a simpler more straightforward metrics emission has been added, inline with the method that needs measurement

Screenshots

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