Fixing w3c baggage support in opentelemetry-instrumentation-aws-lambda

[dtorok]

Description

Fixing baggage support in opentelemetry-instrumentation-aws-lambda package.

After determining the parent context (_determine_parent_context()), it was only used to create the wrapper span, but wasn't attached to the global context. Although the start_as_current_span() call attaches the span's context, but because the SpanContext only contains span-related info, the baggage content was lost, and the propagators couldn't pick it up.
This change attaches/detaches the baggage to the context in a try/finally clause. Other instrumentations do the same either directly, or through _start_internal_or_server_span().

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Implemented a unit test, and ran all the relevant tests:

tox -e lint-instrumentation-aws-lambda
tox -e py38-test-instrumentation-aws-lambda
tox -e py39-test-instrumentation-aws-lambda
tox -e py310-test-instrumentation-aws-lambda
tox -e py311-test-instrumentation-aws-lambda

Does This PR Require a Core Repo Change?

• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: dtorok / name: Daniel Torok (eb7f7ec, 47eb88f, d74534f, 6c93900)

[wangzlei]

LGTM!

@nemoshlag @NathanielRN

[xrmx]

@dtorok please rebase and move the CHANGELOG entry to a new unreleased section

[tammy-baylis-swi]

Lgtm, please resolve the small merge conflict after Changelog updated by merge from another PR.