Fix default value for start date in GitlabSubscription being static

Merged Heinrich Lee Yu requested to merge 11432-fix-gitlab-subscription- into master

What does this MR do?

Makes the default value for start_date in GitlabSubscription dynamic per instance.

Previously, it was fixed to the value of Date.today when the class was loaded.

Does this MR meet the acceptance criteria?

Conformity

Performance and testing

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

Closes #11432 (closed)

Edited by Coung Ngo