Make License-Scanning backward compatible

What does this MR do?

Recently, we updated this legacy template to make it fail when used, forcing our user to update their configuration. We saw at GitLab today some pipeline suddenly becoming red, causing a lot of trouble already. I don't think we should "punish" users who don't follow all our deprecation notices, especially when there's a way to keep the same file and yet use the new features of License-Scanning. It's a bit late for GitLab.com, but we can still save the on-prem users.

The cost of keeping this file as it is negligible, and will avoid a lot of dissatisfaction from our users.

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

@gonzoyumo @NicoleSchwartz What do you think? /cc @brytannia