Introduce support for ETag validation in S3.DeleteObjects

[barak-itkin]

This MR introduces support for ETag validation of objects in the DeleteObjects (batch) API Call via the Objects[].ETag parameter, in a similar fashion to what's already supported in DeleteObject (single object) via the IfMatch parameter.

The test itself is almost a duplicate of the test in the same file for DeleteObject, and was verified against my AWS account.

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.29%. Comparing base (7dc0838) to head (630cd82).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
moto/s3/responses.py	86.66%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (86.66%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10130      +/-   ##
==========================================
- Coverage   93.29%   93.29%   -0.01%     
==========================================
  Files        1336     1336              
  Lines      121804   121813       +9     
==========================================
+ Hits       113635   113641       +6     
- Misses       8169     8172       +3     

Flag	Coverage Δ
servertests	27.87% <6.66%> (-0.01%)	⬇️
unittests	93.26% <86.66%> (-0.01%)	⬇️

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