Add instrumentation for aiopg

[sartx]

Hi, everyone!

This is opentelemetry integration to aiopg. It based on dbapi extension with async wrapper and instumentor.

[sartx]

I signed it

[cnnradams]

It seems like a significant amount of the instrumentation code here very similar to what's in the dbapi instrumentation library. I understand that because aiopg is async we won't be able to fully use the dbapi helpers, but is there some way to break down the dbapi functions so aiopg can generally use them instead of copying the code? Would make this much easier to review

[sartx]

@cnnradams
Thanks for comment. It really looks like that it is better to extend dbapi integration. Firstly I tried to do this. But in the implementation I met a couple of difficulties:

1. Async function can be called only from another async function. In dbapi def wrap_connect_ is a synchronous function.
   In def wrap_connect appears need to determine what kind of function we want to wrap. It can be done by funciton iscoroutinefunction in inspect module - it works only with async def syntax, but aiopg use it only since 1.0.0 version, older versions use @coroutine decorators and it becomes more difficult to define that funciton is async.
   Another way is manual throwing arg, which defines type of wrapped function - but it needs throwing it from trace_integration and wrap_connect.

2. dbapi extension uses wrapt lib, which does not wrap async magic methods, as 'await', 'aenter', 'aexit' and so on. I extended ObjectProxy by creating AsyncObjectProxy. Replace ObjectProxy by AsyncObjectProxy in dbapi does not look like a big problem.

3. In DatabaseApiIntegration we need to add async version fordef wrapped_connection function

4. We can not reuse def get_traced_connection_proxy function, because calling wrapped cursor function won't wrap def _cursor function of aiopg, but we need to do it.

5. Most of classes need to add async version for methods, as TracedCursorProxy, TracedCursor.

All this things will make dbapi extension is too complex as for me.

But I have an idea how to reduce duplicated code.

1. Inherit AiopgIntegration from DatabaseApiIntegration - it give us opportunity to reuse def get_connection_attributes
2. In dbapi extension take out from method TracedCursor.traced_execution setting span attributes to separate method
   If you agree, then I will do this revision as part of this PR

[cnnradams]

But I have an idea how to reduce duplicated code.

1. Inherit AiopgIntegration from DatabaseApiIntegration - it give us opportunity to reuse def get_connection_attributes
2. In dbapi extension take out from method TracedCursor.traced_execution setting span attributes to separate method
   If you agree, then I will do this revision as part of this PR

Sounds like a good plan to me! Also thanks for the explanation, it definitely seems like trying to use all of dbapi would be way too much hassle for what its worth.

[codeboten]

Thanks for the PR, I updated the package name to opentelemetry-instrumentation-aiopg.

[sartx]

@codeboten @lzchen Thanks for review
@cnnradams Thanks for promoting of this PR. Now it is waiting your review.