feat: support sending requests with the 'external_idp' type

[rli]

Problem

External IdP request behavior is not quite builderId and not quite like identityCenter

Solution

Add new type to runtimes and handle in language-serers

Related: aws/language-server-runtimes#679

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 70.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.87%. Comparing base (e0941d1) to head (af18d89).

Files with missing lines	Patch %	Lines
...codewhisperer/src/shared/streamingClientService.ts	61.53%	5 Missing ⚠️
...p-codewhisperer/src/shared/codeWhispererService.ts	25.00%	3 Missing ⚠️
...mazonQServiceManager/AmazonQTokenServiceManager.ts	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2247      +/-   ##
==========================================
+ Coverage   59.71%   59.87%   +0.16%     
==========================================
  Files         254      254              
  Lines       56245    56262      +17     
  Branches     3337     3364      +27     
==========================================
+ Hits        33584    33688     +104     
+ Misses      22597    22509      -88     
- Partials       64       65       +1     

Flag	Coverage Δ
unittests	59.87% <70.00%> (+0.16%)	⬆️

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