No groups in multi-tenant setup

[rhafer]

Userstory

As admin, i want disallow groups function in multi-tenancy setup.

Value

Provide MVP for multi-tenancy setup

Description

Per tenant groups are currently not implemented as they were not in scope for the first iteration. We need to either implement that or make sure that OpenCloud is able to run without errors when the groups service is disabled.

Acceptance Criteria

• Groups are not shown in the share dialog
• Document that groups are not supported ( needs stay to be disabled in autoprovisioning config )

Implementation Detail

• this is not descions against groups in multi-tenancy setup, just the awareness
• using the flag for configuration Introduce a multi-tenancy enablement configuration switch #1458
• if multi-tenancy is not possible create empty results

[db-ot]

CC @micbar

[rhafer]

opencloud-eu/reva#360 introduced the null group manager. We agreed that that is enough to fulfill the multi-tenancy requirements.