Redis connection refactor

[tylerhutcherson]

For ultimate clarity and safety of our library, the decision was made to separate the sync and async search index modules for now until we can better utilize the redis-py client to serve both needs simultaneously.

This PR splits SearchIndex and AsyncSearchIndex into two classes. It also refactors the way RedisVL handles Redis connections (much more lightweight) and makes some major improvements to the overall documentation on these topics.

[codecov-commenter]

Codecov Report

Attention: 47 lines in your changes are missing coverage. Please review.

Comparison is base (8a55e35) 77.32% compared to head (0583540) 78.90%.

Files	Patch %	Lines
redisvl/index.py	75.00%	32 Missing ⚠️
redisvl/redis/utils.py	65.38%	9 Missing ⚠️
redisvl/redis/connection.py	92.85%	3 Missing ⚠️
redisvl/schema/schema.py	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #104      +/-   ##
==========================================
+ Coverage   77.32%   78.90%   +1.57%     
==========================================
  Files          23       24       +1     
  Lines        1429     1474      +45     
==========================================
+ Hits         1105     1163      +58     
+ Misses        324      311      -13     

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[tylerhutcherson]

Will address the concerns from #88