Group Deploy Tokens interface

What does this MR do?

This MR is part of the development of group deploy tokens. This MR does two things:

• it adds a Deploy Token section in Group > Settings > CI/CD.
• as it reuses the same interface as for the project-scoped deploy tokens, a lot of refactoring was done in this MR:
  • partials used in the project deploy token views were moved to the app/views/shared and reused for the group deploy token views.
  • concerns and rspec shared examples were created for refactoring purposes.

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

Relates to #21765 (closed)