Allow host class of Limitable to extend logic [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This MR adds an extensibility point to Limitable so that the host class can use its state to determine which e.g. limit_name to return.

This MR is required for !60157 (merged) since we need to limit the number of runners that are registered per-instance, per-group or per-project, depending on the type of registration token we're using. Since we have a single model to represent the 3 types of runner scopes, we need to extend the Limitable class to ask Ci::Runner about those details depending on its state.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because this is not a user-facing feature.
• Documentation (if required)
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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

Part of #321368