build: refactor afw & proxy into workers/

[hallvictoria]

Description

Moves azure_functions_worker and proxy_worker into workers/

• No code changes (eg: no changes to import statements)
• Only changes are to pipelines that now need to cd into workers/ to run tests and builds

Sample official build with these changes: https://azfunc.visualstudio.com/internal/_build/results?buildId=225513&view=results

Fixes #

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• New Unit tests were added for the changes made and CI is passing.

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