[Remote Store] Integration tests at repository level

[gbbafna]

We don't have Integration tests in s3 repository plugin which uses remote store. We need to add it as remote store repositories has different characteristics and expectations like

1. Reload repository support
2. Remote Download Stats integration.

[linuxpi]

[Storage Triage - attendees 1 2 3 4 5 6 7 8 9 10 11 12]

@gbbafna Thanks for opening this. Please add more details to the issue. CC: @vikasvb90