Add Project Feature to Project Migration

What does this MR do and why?

Related to #339416 (closed)

⚠ this feature is behind bulk_import_projects feature flag that is currently off by default (and disabled on .com).

This MR adds Project Feature migration when using Group Migration that includes projects (https://docs.gitlab.com/ee/user/group/import/).

Please note that on the screencast below you might notice that LFS and Package settings are not the same value. This is because those 2 settings come from project model (lfs_enabled & packages_enabled) and are not coming from project_feature model.

Screenshots or screen recordings

projectfeature

How to set up and validate locally

1. Feature.enable(:bulk_import).
2. Feature.enable(:bulk_import_projects).
3. Create a top level group and project in it.
4. Update project feature settings on project general settings page
5. Go to /groups/new#import-group-pane page and enter instance url and access token (needs to be api & read_repository scope).
6. Select newly created group and click Import.
7. Wait for Group import to complete and verify imported project feature settings