fix: add region validation using DNS Host label regex

[trivikr]

Issue #, if available:
From v2: aws/aws-sdk-js#3368
Internal issue JS-1834

Description of changes:
adds region validation using DNS Host label regex

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[codecov-commenter]

Codecov Report

Merging #1402 into master will increase coverage by 0.40%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1402      +/-   ##
==========================================
+ Coverage   79.08%   79.48%   +0.40%     
==========================================
  Files         287      296       +9     
  Lines       11155    11388     +233     
  Branches     2360     2434      +74     
==========================================
+ Hits         8822     9052     +230     
- Misses       2333     2336       +3     

Impacted Files	Coverage Δ
...dential-provider-imds/src/fromContainerMetadata.ts
...edential-provider-imds/src/remoteProvider/retry.ts
...al-provider-imds/src/remoteProvider/httpRequest.ts
...rovider-imds/src/remoteProvider/ImdsCredentials.ts
...ider-imds/src/remoteProvider/RemoteProviderInit.ts
...edential-provider-imds/src/fromInstanceMetadata.ts
...provider-imds/dist/cjs/src/fromInstanceMetadata.ts	100.00% <0.00%> (ø)
packages/is-array-buffer/dist/cjs/src/index.ts	100.00% <0.00%> (ø)
packages/util-buffer-from/dist/cjs/src/index.ts	100.00% <0.00%> (ø)
...eProvider/src/remoteProvider/RemoteProviderInit.ts	100.00% <0.00%> (ø)
... and 11 more

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