Provide API to update a software license policy

What does this MR do?

This change is a continuation of the work started in !19598 (merged). This MR adds the ability to change the classification for any software license policy. The emphasis of this work is focused on the backend changes to ensure the required functionality is satisfied. The UI still needs ❤.

Screenshots

The HAML markup has been removed to reduce the size of this MR.

#34826 (closed)

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

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