Cloud License: Activation to receive license instead of authentication token

What does this MR do?

Previously !51450 (merged) established an activation mechanism involves persisting an authentication token. This will be changed because we want to align cloud license with seat link, dropping authentication token, and use license directly.

The cloud license proposal step 2 outlines activation process (GitLab instance's side)

This is mirroring the changes in https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/2864

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 behind feature flag.
• [-] 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.
• 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

Related to #301032