Disable scanner commands and background jobs for unscannable storages

[PVince81]

In the case of non-scannable storages like primary object store, we need to disable automatically:

• background jobs related to background scanning
• occ commands

Maybe the jobs/commands in question can still be listed but should not do anything when run.

[ownclouders]

GitMate.io thinks possibly related issues are #20435 (Customize scanner for root storage to disable scanning.), #23277 (disable external storages), #22887 (non-ending background job), #26760 (InfoParser not properly parsing single background-job, single command, etc), and #16826 (Debounce expiration background jobs).