pubsub/awssnssqs: add support for AWS SDK v2 for URL openers

[vangent]

Updates #3026.

[codecov]

Codecov Report

Merging #3076 (b63459d) into master (cfbf972) will increase coverage by 0.02%.
The diff coverage is 76.92%.

@@            Coverage Diff             @@
##           master    #3076      +/-   ##
==========================================
+ Coverage   71.89%   71.92%   +0.02%     
==========================================
  Files         112      112              
  Lines       13835    13853      +18     
==========================================
+ Hits         9947     9964      +17     
- Misses       3190     3191       +1     
  Partials      698      698              

Impacted Files	Coverage Δ
pubsub/awssnssqs/awssnssqs.go	85.97% <76.92%> (+0.42%)	⬆️
server/health/sqlhealth/sqlhealth.go	61.90% <0.00%> (-19.05%)	⬇️
docstore/docstore.go	89.56% <0.00%> (+1.79%)	⬆️
internal/retry/retry.go	100.00% <0.00%> (+11.76%)	⬆️

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