Add botocore instrumentation

[ocelotl]

Fixes #675

[codeboten]

Thanks for doing this work, just a couple of changes requested. Looks like there's also an entry missing in the docs.

[codeboten]

Thanks for addressing my comments, the code looks good. Looks like it's missing an entry in the docs.

[toumorokoshi]

Approving although I think there's a few improvements around the data structure choices, looks good!

I wanted to raise a couple questions before we finish it up:

Merge with boto instrumentation?

A lot of code is shared with the boto instrumentation, due to what I assume is relying on data structures that boto exposes that are actually components of botocore. Does it make sense to combine instrumentations? This may help with situations like ensuring botocore instrumentation and boto instrumentation don't overlap each other.

Boto + Botocore auto-instrumentation

I think one can imperatively choose not to instrument boto / botocore depending on what level of granularity they want. But how will this work with auto-instrumentation?

Also I wonder what value instrumenting boto provides if botocore already provides a majority of the context by wrapping the _make_api_call, which I presume is what is called by the boto authenticated requests.

[toumorokoshi]

@ocelotl if you can follow up quick with the botocore / boto refactor, that would be great. Also a strategy that allows both to work in tandem with auto-instrumentation without double logging all spans.