IndexSchema refactor and async collapse

[tylerhutcherson]

This PR introduces a new user space class, IndexSchema. This effort to refactor the index schema is key for us to be able to enable "wrappability" and extensibility of RedisVL with other integration efforts (i.e. LangChain), and also improve the UX of working with the tool overall.

A few changes:

• SearchIndex now expects the schema to be provided on init, or built with some of the constructors (common).
• SearchIndex now optionally expects redis_url or redis_client
• An initial MVP of the RedisConnection class was built to support working with both sync and async connections from redis-py. A better implementation will be coming in the near term.
• Async and Sync search index were combined. No more AsyncSearchIndex class here.
• Other updates and docs improvements.

Adding link to current notes on the schema spec: https://docs.google.com/document/d/1vkShf9PoQd1FnjYa2PpKhcgk8FW9WZGi_KpCuoDtvEY/edit?usp=sharing

[Spartee]

Great start. Lots of thoughts on here. Would be good to sync on this and what you're doing with collapsing the interfaces.

Biggest theme here is reduction in code duplication, I think we can collapse

• SchemaModel
• FieldsModel
• SchemaGenerator

into

• Schema

Let me know what you think. Great start!

[codecov-commenter]

Codecov Report

Attention: 63 lines in your changes are missing coverage. Please review.

Comparison is base (9b870ca) 80.54% compared to head (e6e4b01) 78.64%.

Files	Patch %	Lines
redisvl/utils/utils.py	15.38%	22 Missing ⚠️
redisvl/schema/schema.py	87.12%	17 Missing ⚠️
redisvl/utils/connection.py	72.22%	10 Missing ⚠️
redisvl/index.py	88.40%	8 Missing ⚠️
redisvl/llmcache/semantic.py	86.11%	5 Missing ⚠️
redisvl/schema/fields.py	98.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev      #85      +/-   ##
==========================================
- Coverage   80.54%   78.64%   -1.91%     
==========================================
  Files          19       21       +2     
  Lines        1203     1283      +80     
==========================================
+ Hits          969     1009      +40     
- Misses        234      274      +40     

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