Redis ACL/Username and Database Support

[oxzi]

Is your feature request related to a problem? Please describe.

There were requests for both ACL and database support for the Redis server, e.g., Icinga/icingadb#529, Icinga/icingadb#676, Icinga/icinga2#9536.

I have started implementing this in the icinga-go-library, being available in Icinga DB after the next icinga-go-library release, and created a PR in Icinga 2, Icinga/icinga2#10102. To make this feature fully usable, Icinga DB Web also needs to support authentication via username and selecting a database directly after establishing the connection.

Describe the solution you'd like

As it seems, Icinga DB Web uses Predis as its Redis library. Fortunately, it supports both username authentication and database selection, https://github.com/predis/predis/wiki/Connection-Parameters. Thus it "just" needs to be made configurable.

Describe alternatives you've considered

N/A

Additional context

• Document Redis username and database icingadb#782
• Username support in redis configuration icingadb#529
• Redis DB Index should be configurable icingadb#676
• redis: Configurable Database icinga-go-library#50
• redis: Configurable Username icinga-go-library#52
• Redis username support for icingadb feature icinga2#9536
• Icinga DB: Config no_user_modify and Support Redis username authentication icinga2#10102