[Core] implement redis cache mode (#1222)

* implement redis cache mode, if redis_url is set in the llm_config then
it will try to use this.  also adds a test to validate both the existing
and the redis cache behavior.

* PR feedback, add unit tests

* more PR feedback, move the new style cache to a context manager

* Update agent_chat.md

* more PR feedback, remove tests from contrib and have them run with the normal jobs

* doc

* updated

* Update website/docs/Use-Cases/agent_chat.md

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* update docs

* update docs; let openaiwrapper to use cache object

* typo

* Update website/docs/Use-Cases/enhanced_inference.md

Co-authored-by: Chi Wang <wang.chi@microsoft.com>

* save previous client cache and reset it after send/a_send

* a_run_chat

---------

Co-authored-by: Vijay Ramesh <vijay@regrello.com>
Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>
Co-authored-by: Chi Wang <wang.chi@microsoft.com>