Define resource group at Ci::Processable level

What does this MR do?

We're going to support Resource Group keyword for any job-types, including build-type and bridge-type. This MR moves the resource group implementations from Ci::Build to Ci::Processable, which is super class of both Ci::Build and Ci::Bridge.

This MR doesn't change any business logic, but just refactoring. Users cannot still use resource group in bridge jobs (It'll be no-op).

Related #39057 (closed)

Screenshots (strongly suggested)

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