feat(aiohttp): add client integration (backport #3362)

[mergify]

This is an automatic backport of pull request #3362 done by Mergify.
Cherry-pick of 2ac1fc9 has failed:

On branch mergify/bp/0.x/pr-3362
Your branch is up to date with 'origin/0.x'.

You are currently cherry-picking commit 2ac1fc95.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .circleci/config.yml
	modified:   ddtrace/contrib/aiohttp/__init__.py
	new file:   ddtrace/contrib/trace_utils_async.py
	modified:   docs/index.rst
	new file:   releasenotes/notes/aiohttp-98ae9ce70dda1dbc.yaml
	modified:   riotfile.py
	modified:   tests/contrib/aiohttp/conftest.py
	new file:   tests/contrib/aiohttp/test_aiohttp_client.py
	modified:   tests/contrib/config.py
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_200_request.json
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_200_request_post.json
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_500_request.json
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_configure_global_service_name_env.json
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_configure_service_name_pin.json
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_trace_multiple.json
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_trace_parenting.json
	new file:   tests/snapshots/tests.contrib.aiohttp.test_aiohttp_client.test_trace_query_string.json

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   ddtrace/contrib/aiohttp/patch.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[mergify]

@mergify[bot] this pull request is now in conflict 😩