front: enable project grants

[SharglutDev]

close #17988

TODO:

• rebase PR with dev when front: permissions on rolling stock #17855 is merged (and the feature branch is closed), there might be some conflicts
• in the meantime, keep working on commit 2 and 3 and check grants when feature flag is on

Test the PR:

To add new users

• Add user:
  docker exec osrd-editoast editoast user add --skip-if-exists 'Jane Doe' 'jane.doe@example.com'
• Pass it operational studies role:
  docker exec osrd-editoast editoast roles add 'jane.doe@example.com' OperationalStudies

• Activate the project grants feature flag
• Open a project, the grants manager should be present under the project image
• Impersonate Jane Doe, we should get a 403 and be redirected to the 403 error page
• Go back to home page and logout from Jane Doe and open a scenario
• Impersonate Jane Doe, we should get a 403 and be redirected to the 403 error page (if we don't have access to the project containing the scenario, we should not be able to access the scenario)
• Logout from Jane and repeat when on a study and logout from Jane
• Go back to a project, open the grant manager and try to add grant to Jane Doe
• The only possible option in the select should be "total access"
• Give total access to Jane Doe and go back to the home page
• Impersonate Jane
• Open the project list, we should only see the project we just gave grants to
• Open the project, we should have access to it, its studies and scenarios and be able to edit them
• Bonus: while the feature flag still exists (if not to much work but really important as long as it work when we remove the feature flag) go back to home page, remove the feature flag for project grants; we should see every projects available