fix(signature-v4): add secrets to signing key cache key

[AllanZhengYP]

Fixes #1002

Description of changes:
This change fix the issue that signing key is not refreshed between requests with only different secret access keys. I added a hash of both access key id and secrete access key as the cache key is signing keys.

However, previously we cached pending promise of signing keys, but now we only cache the resolved promise of signing keys. So it's safer but may have wild performance implication. We can optimize this after we have benchmark metrics of this module.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-io]

Codecov Report

Merging #1776 (0dc9971) into master (de75f7e) will decrease coverage by 0.49%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1776      +/-   ##
==========================================
- Coverage   79.77%   79.28%   -0.50%     
==========================================
  Files         325      367      +42     
  Lines       12087    15116    +3029     
  Branches     2553     3221     +668     
==========================================
+ Hits         9643    11985    +2342     
- Misses       2444     3131     +687     

Impacted Files	Coverage Δ
protocol_tests/aws-json/models/models_0.ts	79.36% <0.00%> (-20.64%)	⬇️
packages/util-user-agent-node/src/index.ts	88.88% <0.00%> (-11.12%)	⬇️
protocol_tests/aws-restjson/models/models_0.ts	89.43% <0.00%> (-10.57%)	⬇️
...rotocol_tests/aws-restxml/protocols/Aws_restXml.ts	64.10% <0.00%> (-2.15%)	⬇️
...ackages/node-http-handler/src/node-http-handler.ts	98.00% <0.00%> (-2.00%)	⬇️
packages/middleware-sdk-sqs/src/send-message.ts	86.66% <0.00%> (-0.84%)	⬇️
protocol_tests/aws-query/protocols/Aws_query.ts	66.34% <0.00%> (-0.38%)	⬇️
...kages/middleware-sdk-sqs/src/send-message-batch.ts	92.30% <0.00%> (-0.29%)	⬇️
...kages/fetch-http-handler/src/fetch-http-handler.ts	9.30% <0.00%> (-0.23%)	⬇️
protocol_tests/aws-ec2/protocols/Aws_ec2.ts	66.93% <0.00%> (-0.01%)	⬇️
... and 188 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 388b180...0dc9971. Read the comment docs.

[trivikr]

LGTM! Added some nit for unit tests

[AllanZhengYP]

Rebase it to pass the Java test

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs and link to relevant comments in this thread.