Avoid loading the request stream to retrieve context

[dfangl]

Issue

We are currently loading the flask request for a thread every time we call get_request_context(), even though we might find it in the thread local variable anyway.

This leads to the request streams being read, if you access methods like "get_region_from_request_context`, and the streams not being available anymore.

Solution

Instead of loading both, and then iterating, we will now load while iterating. This means, if the threadlocal request context is set, we will not call get_flask_request_for_thread, and therefore not load the request.

While this is still implicit, and it is still possibly loading the request into a flask request, it provides a reasonable improvement until we can get rid of the flask context one and for all.

[thrau]

that's a wicked find! LGTM

[coveralls]

coverage: 82.792% (+0.02%) from 82.769% when pulling 2edd69a on avoid-stream-loading into a83e15f on master.

[github-actions]

LocalStack Community integration with Pro

       2 files         2 suites   1h 24m 13s ⏱️
2 101 tests 1 815 ✔️ 286 💤 0 ❌
2 102 runs  1 815 ✔️ 287 💤 0 ❌

Results for commit 2edd69a.