test(client-cognito-identity): add cross platform integ tests

[AllanZhengYP]

Similar to #1296 but for cognito identity client.

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[codecov-commenter]

Codecov Report

Merging #1309 into master will increase coverage by 4.44%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1309      +/-   ##
==========================================
+ Coverage   73.04%   77.49%   +4.44%     
==========================================
  Files         287      286       -1     
  Lines       12730    11899     -831     
  Branches     2922     2600     -322     
==========================================
- Hits         9299     9221      -78     
+ Misses       3431     2678     -753     

Impacted Files	Coverage Δ
packages/region-provider/src/fromEnv.ts	100.00% <0.00%> (ø)
protocol_tests/aws-ec2/runtimeConfig.ts	100.00% <0.00%> (ø)
protocol_tests/aws-json/runtimeConfig.ts	100.00% <0.00%> (ø)
packages/property-provider/src/memoize.ts	100.00% <0.00%> (ø)
protocol_tests/aws-query/runtimeConfig.ts	100.00% <0.00%> (ø)
protocol_tests/aws-ec2/EC2ProtocolClient.ts	92.30% <0.00%> (ø)
protocol_tests/aws-restxml/runtimeConfig.ts	100.00% <0.00%> (ø)
protocol_tests/aws-restjson/runtimeConfig.ts	100.00% <0.00%> (ø)
protocol_tests/aws-json/JsonProtocolClient.ts	92.30% <0.00%> (ø)
packages/middleware-retry/src/configurations.ts	100.00% <0.00%> (ø)
... and 13 more

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[alexforsyth]

LGTM

[github-actions]

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