Deprecate Import bare repositories

Deprecation Summary

Gitlab provides a rake task to import a directory tree of repositories into a gitlab instance. These repositories must have been part of a gitlab instance previously because it relies on the specific directory structure or a specific custom git setting in order to work (gitlab.fullpath). https://docs.gitlab.com/ee/raketasks/import.html

This importer has some problems:

It only knows about project and project wiki repos. So will not handle design repos, group wikis, or snippets.
It allows users to import non-hashed storage projects even though these aren't supported.
It relies on having git config gitlab.fullpath set which will not be supported by gitaly cluster.

There are better supported alternatives to migrate repositories to another gitlab instance or to import repositories from a non-gitlab source

Breaking Change

This is a breaking change. Users should use the documented migration/import steps above.

Affected Topology

Self-managed users.

Affected Tier

Free
Premium
Ultimate

Checklists

Labels

This issue is labeled deprecation, and with the relevant ~devops::, ~group::, and ~Category: labels.
This issue is labeled breaking change if the removal of the deprecated item will be a breaking change.

Timeline

Please add links to the relevant merge requests.

As soon as possible, but no later than the third milestone preceding the major release (for example, given the following release schedule: 14.8, 14.9, 14.10, 15.0 – 14.8 is the third milestone preceding the major release):
- A deprecation announcement entry has been created so the deprecation will appear in release posts and on the general deprecation page.
- Documentation has been updated to mark the feature as deprecated.
On or before the major milestone: A removal entry has been created so the removal will appear on the removals by milestones page and be announced in the release post.
On the major milestone:
- The deprecated item has been removed.
- If the removal of the deprecated item is a breaking change, the merge request is labeled breaking change.

Mentions

Your stage's stable counterparts have been @mentioned on this issue. For example, Customer Support, Customer Success (Technical Account Manager), Product Marketing Manager.
- To see who the stable counterparts are for a product team visit product categories
  - If there is no stable counterpart listed for Sales/CS please mention @timtams
  - If there is no stable counterpart listed for Support please mention @gitlab-com/support/managers
  - If there is no stable counterpart listed for Marketing please mention @cfoster3
Your GPM has been @mentioned so that they are aware of planned deprecations. The goal is to have reviews happen at least two releases before the final removal of the feature or introduction of a breaking change.

Deprecation Milestone

%15.8 ?

Planned Removal Milestone

%16.0