Add pagination support to import_projects application

What does this MR do?

This MR adds pagination support for our importers Vue UI.

It supports two modes:

• #222889 (closed) when default gitlab pagination headers are present (not yet supported by backend
• #233059 (closed) when no pagination headers present at all (legacy pagination used only in bitbucket server importer)

Screenshots

demo

Video includes me faking gitlab API response for first use case and normal use case for second

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