pubsub/awssnssqs: fix docs/examples/tests to show SNS ARN in path, not hostname

[vangent]

Fixes #2647.

[codecov]

Codecov Report

Merging #2648 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2648      +/-   ##
==========================================
- Coverage   66.97%   66.95%   -0.02%     
==========================================
  Files         134      134              
  Lines       15584    15584              
==========================================
- Hits        10437    10434       -3     
- Misses       4394     4399       +5     
+ Partials      753      751       -2

Impacted Files	Coverage Δ
pubsub/awssnssqs/awssnssqs.go	85.45% <ø> (ø)	⬆️
server/health/sqlhealth/sqlhealth.go	61.9% <0%> (-19.05%)	⬇️
pubsub/pubsub.go	93.41% <0%> (+1.56%)	⬆️

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