OpenTelemetry support

[pquentin]

Here are the pull requests to backport:

• [ ] https://github.com/elastic/elasticsearch-py/pull/2457
• [ ] https://github.com/elastic/elasticsearch-py/pull/2466
• [ ] https://github.com/elastic/elasticsearch-py/pull/2470
• [ ] https://github.com/elastic/elasticsearch-py/pull/2479
• [ ] https://github.com/elastic/elasticsearch-py/pull/2482
• [ ] https://github.com/elastic/elasticsearch-py/pull/2490
• [ ] https://github.com/elastic/elasticsearch-py/pull/2491

[pquentin]

Closing, #52 already existed.