Add Redis Sentinel Authentication Support (#19213)

Add Redis Sentinel Authentication Support (#19213)

Gitea was not able to supply any authentication parameters to it. So this brings support to do that, along with some light extraction of a couple of bits into some separate functions for easier testing.

I looked at other libraries supporting similar RedisUri-style connection strings (e.g. Lettuce), but it looks like this type of configuration is beyond what would typically be done in a connection string. Since gitea doesn't have configuration options for manually specifying all this redis connection detail, I went ahead and just chose straightforward names for these new parameters.