docs: add docs with differences from the APM Python agent

[xrmx]

What does this pull request do?

Document some of the differences between the APM Python agent and EDOT.

Related issues

Closes #123

[xrmx]

@akhileshpok Would appreciate a review of this from your point of view. Maybe we are overpromising :)

[colleenmcginnis]

I left some suggestions below. Feel free to take them or leave them as you see fit!

[colleenmcginnis]

Can we be more specific about how to request additional instrumentations? Maybe opening an issue using the feature request template?

Suggested change

	Not all instrumentations we have in Elastic APM Python Agent have an OpenTelemetry counterpart. But we may port them if they are requested by users.
	Not all instrumentations we have in the Elastic APM Python agent have an OpenTelemetry counterpart. If you would like to see a specific instrumentation ported to OpenTelemetry, submit a [feature request](https://github.com/elastic/elastic-otel-python/issues/new?template=Feature_request.md).

[xrmx]

I would prefer to get these from support / product people instead of github users though 😅

[colleenmcginnis]

At the moment of writing these docs

Since we're suggesting these docs may become out of date, can we also point them somewhere to see the latest list of libraries with an OpenTelemetry instrumentation? Maybe https://github.com/open-telemetry/opentelemetry-python-contrib/tree/main/instrumentation#readme? Or is there somewhere in the code in this repo?

Suggested change

	For the latest list of supported OpenTelemetry instrumentations, visit the [OpenTelemetry Python Contrib repo](https://github.com/open-telemetry/opentelemetry-python-contrib/tree/main/instrumentation#readme).

[xrmx]

I see the issue but we may decide to not ship some of them or ship some instrumentations that are not available there. So I prefer to don't link it.

[akhileshpok]

Are there any other features that are only supported in the classic Python Agent, e.g., compressed spans? We should list any feature that is only supported in the classic Python Agent in this doc as well. Thanks

[xrmx]

Are there any other features that are only supported in the classic Python Agent, e.g., compressed spans? We should list any feature that is only supported in the classic Python Agent in this doc as well. Thanks

Updated the document with missing integration with structured logging, span compression and breakdown metrics.