Add a function URL enabling public access to Lambda function

[aaarendt]

This PR adds a function URL enabling a publicly accessible dedicated HTTPS endpoint. Prior to this users required having access to AWS credentials which we don't want to distribute.

[codecov]

Codecov Report

❌ Patch coverage is 16.12903% with 52 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.52%. Comparing base (7d9c6f4) to head (7c88fa1).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
snowexsql/lambda_client.py	18.51%	44 Missing ⚠️
snowexsql/lambda_handler.py	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #209      +/-   ##
==========================================
- Coverage   60.25%   59.52%   -0.73%     
==========================================
  Files          23       23              
  Lines        1195     1218      +23     
==========================================
+ Hits          720      725       +5     
- Misses        475      493      +18     

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[jomey]

Mostly minor comments and curious thoughts