1.39.1 candidate -> release/1.39

[pjenvey]

This would be a 1.39.1 sans the boto3 integration and the small rust metrics addition.

Fast-forwarded to fa47b5c and cherry picked everything else. Had one minor conflict in test_endpoint.test_delete_db_error w/ an easy fix.

[codecov-io]

Codecov Report

Merging #1082 into release/1.39 will decrease coverage by 0.01%.
The diff coverage is 99.2%.

@@               Coverage Diff                @@
##           release/1.39    #1082      +/-   ##
================================================
- Coverage         99.75%   99.73%   -0.02%     
================================================
  Files                56       58       +2     
  Lines              8888     9063     +175     
================================================
+ Hits               8866     9039     +173     
- Misses               22       24       +2

Impacted Files	Coverage Δ
autopush/router/gcmclient.py	100% <100%> (ø)
autopush/router/gcm.py	100% <100%> (ø)	⬆️
autopush/router/apnsrouter.py	100% <100%> (ø)	⬆️
autopush/web/webpush.py	100% <100%> (ø)	⬆️
autopush/tests/test_integration.py	100% <100%> (ø)	⬆️
autopush/tests/test_gcmclient.py	100% <100%> (ø)
autopush/tests/test_router.py	100% <100%> (ø)	⬆️
autopush/tests/test_web_webpush.py	100% <100%> (ø)	⬆️
autopush/ssl.py	96.07% <50%> (-3.93%)	⬇️
... and 1 more

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