Add configuration option to `RedisCache` to allow read-only access

Currently, `RedisCache` resets expiry for keys on every read (https://github.com/dotnet/aspnetcore/blob/main/src/Caching/StackExchangeRedis/src/RedisCache.cs#L293 and in the async version as well).

When using Redis as a session storage, this can lead to sessions getting invalidated unnecessarily on Redis failover. During a new leader election read-only access is preserved which would allow existing clients to continue. However due to the `EXPIRE` command being issued alongside the read, the read command will fail.

This might be desired behaviour in other circumstances. For a session storage solution it would be fine to just ignore the exception on expire and carry on. In the case that Redis writes do not become available within expiry time, the session would then expire. It would also still expire when attempting other writes.

A configuration option for the cache would be nice to allow expire to fail. Otherwise, changing the variables in the class to `protected` so sensible overrides are possible might be another solution.