Integrate 'elastic-transport-python'

[sethmlarson]

Integrates the development version of https://github.com/elastic/elastic-transport-python into the 8.0 branch.

• Removes all transport/connection/pool classes from the package
• Creates a new "BaseClient" which adds per-request configuration of transport options via .options().
• Adds a _deprecated_options() function which is added as a part of API generation. This function resolves the deprecated per-request options via the new BaseClient.options() route.
• Moves the product check into Elasticsearch._perform_request().
• Moves the encoding of extra query parameters into Elasticsearch._perform_request()
• Subclasses elastic_transport.JsonSerializer to add the additional encoding options for numpy/pandas/datetimes, etc
• Refactors the exceptions to subclass elastic_transport.ApiError for API errors and to use elastic_transport.TransportError aliases to fill in exceptions that have been moved.
• Documentation will likely fail due to removals, will handle this in a separate PR as more work needs to be done here.

TODO:

• Handle api_key, basic_auth, bearer_auth, and deprecated http_auth.