Allow passing a ConnectionMultiplexerFactory or Instance to AddStackExchangeRedisCache

[evilpilaf]

Currently the implementation for AddStackExchangeRedisCache only lets developers configure a connection string or connection options for setting up the Redis connection, it'd be very useful if it was also possible to pass in a ConnectionMultiplexer instance or factory, dus letting us reuse connections to caches.

This would also let us plug in with OpenTelemetry as it requires a ConnectionMultiplexer object in order to set the telemetry information.

[adityamandaleeka]

@evilpilaf We added this in .NET 6 Preview 5: dotnet/aspnetcore#32266