Add rails caching and/or redis support

[dalen]

It would be great if redis calls could be made into subsegments just as easily as the net/http calls can be. Or adding support for Rails cache reads and writes just like the active record support that is already there.

[haotianw465]

Thank you for the feedback. We will definitely add more coverage on various of operations/libraries over time. We will try to prioritize the work based on the feedback and yours is definitely important to us. Pull request is always welcome if you don't want to wait for the support.