Semantic cache interface update (#80)

Goals of this PR focus on improving the semantic cache interface in
RedisVL

- Remove the ability to pass in an index. This is not the preferred
methodology and currently breaks if the schema doesn't perfectly match
up. Remove references from Docs.
- Naming Conventions:
     - ``index_name`` ➝ ``name``.  Add deprecation warning.
     - ``threshold`` --> ``distance_threshold``. Add deprecation warning.
- For the ``check()`` method, change ``fields`` --> ``return_fields``.
Add deprecation warning.
- Update all main cache interfaces, docs, and tests with these changes.

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Co-authored-by: Sam Partee <sam.partee@redis.com>

Author: tylerhutcherson