Create Nuget shared endpoints

🌵 Context

Please make sure to read the context of !48356 (merged).

This MR is a split of the changes of !48356 (merged)

Related issue: #36423 (closed)

Changelog not needed as it is added in !48356 (merged).

What does this MR do?

• Create a concern with the nuget endpoints that will be shared between the project and group level api.
• Create rspec shared examples that will be re used between the project level and group level api specs.
  • Cleanup the context to remove one (context 'without the need for a license') that is completely unused.
  • Updated the tracking package event call as it uses the class name and we need to keep the same one ('API::NugetPackages')

⚠ Please note that this MR doesn't bring any feature change. It's a simple extraction of Project level endpoints to a concern so that they are more easily shared with the Group level endpoint that is created in !48356 (merged).

Screenshots (strongly suggested)

$ bundle exec spring rspec  spec/requests/api/nuget_packages_spec.rb

on master:

Finished in 3 minutes 30.4 seconds (files took 6.28 seconds to load)
717 examples, 0 failures

on this MR's branch:

Finished in 3 minutes 46.5 seconds (files took 6.73 seconds to load)
717 examples, 0 failures

-> No examples were harmed in this code extraction/move 😺

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