Fix GDK to allow GitLab upload backups to MinIO instance

What does this merge request do and why?

This fix a couple of things to make sure:

• GitLab's Backup Upload configuration is correctly applied
• MinIO supports configuring a Backup bucket
• Creates a Backup bucket when Object Store is enabled
• Move some of the MinIO setup logic from Makefiles to Rake tasks

It also introduces the code required to test rake tasks

How to set up and validate locally

1. Configure gdk.yml to enable object store and define the correct variables for backup upload support:

   object_store:
     backup_remote_directory: 'backups'
     connection:
       provider: AWS
       aws_access_key_id: minio
       aws_secret_access_key: gdk-minio
       region: gdk
       endpoint: http://127.0.0.1:9001
       path_style: true
     console_port: 9002
     consolidated_form: false
     enabled: true
     host: 127.0.0.1
    port: 9001

2. Run gdk reconfigure to check if gitlab.yml is correctly configured
3. Run gdk start and check if minio was enabled and started
4. Run rake gitlab:backup:create and check whether it mentions the backup has been uploaded
5. Visit http://localhost:9002, use the credentials defined in the configuration above and check whether the backup exists in the backups bucket

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.