Add instance-level license template

What does this MR do?

This MR adds an instance-wide template project, and implements the first type of instance-wide templates. The templates are license templates that allow an organization to provide standard organizational licenses for all developers to use in their company projects.

Are there points in the code the reviewer needs to double check?

This is our first contribution, so likely everything.

Why was this MR needed?

This MR closes issue #5986 (closed), and discussions of why this is needed exist there.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?