Update opentelemetry.io documentation with metrics

[aabmass]

• Getting started - https://opentelemetry.io/docs/instrumentation/python/getting-started/
• Manual instrumentation - https://opentelemetry.io/docs/instrumentation/python/manual/
• OTLP and prom exporters should be added - https://opentelemetry.io/docs/instrumentation/python/exporters/
• Update opentelemetry.io cookbook with common view scenarios #2797
• Update opentelemetry.io docs for auto instrumentation once ready #2798

[aabmass]

I split the two remaining tasks into issues since I will be OOO.

[aabmass]

Closing this in favor of the sub-issues