Add versioning support to Terraform backend

What does this MR do?

Creates a new terraform_state_versions table to store a separate file every time a Terraform state is updated, instead of overwriting the same file each time.

Existing Terraform states are unchanged and will need to be migrated at a later date, at which point we can remove the (now duplicated) file and file_store columns on terraform_states.

This is currently invisible to the user (there is no way to access previous versions), a future merge request(s) will expose these via API and UI.

Screenshots

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

#207347 (closed)