## What this PR does
This adds custom indexable fields on core backup resources to enable
filtering by backed-up application. This will later be useful for
displaying backup resources in the dashboard: it will be possible to
filter them with a field selector to display only those backup resources
that are relevant to a given application.
### Release note
```release-note
[backups] Enable filtering backup resources by backed up application for
per-app views of backups.
```
Signed-off-by: Timofei Larkin <lllamnyp@gmail.com>
## What this PR does
This patch creates a new backups.cozystack.io API group which includes
backup-related resources owned exclusively by Cozystack core. A
cronjob-like controller is implemented to create backup jobs that will
be handled by appropriate third-party or external controllers.
### Release note
```release-note
[backups] Implement the core backup API and an accompanying controller.
```
Signed-off-by: Timofei Larkin <lllamnyp@gmail.com>
