Adding bedrock chat completion for anthropic models

[HariniNarasimhan]

Why are these changes needed?

Anthropic models are supported by AWS bedrock. ChatCompletionClient can be created for anthropic bedrock models using this changes. This enables the user to do the following

• Add any anthropic models and version from AWS bedrock
• Can use ChatCompletionClient for bedrock anthropic models

Related issue number

Closes #5226

[HariniNarasimhan]

@microsoft-github-policy-service agree

[ekzhu]

Let's use secrete str for keys and tokens

[codecov]

Codecov Report

Attention: Patch coverage is 45.61404% with 31 lines in your changes missing coverage. Please review.

Project coverage is 78.14%. Comparing base (b3f3731) to head (bf61909).

Files with missing lines	Patch %	Lines
.../autogen_ext/models/anthropic/_anthropic_client.py	27.90%	31 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6170      +/-   ##
==========================================
- Coverage   78.26%   78.14%   -0.13%     
==========================================
  Files         217      217              
  Lines       15669    15723      +54     
==========================================
+ Hits        12263    12286      +23     
- Misses       3406     3437      +31     

Flag	Coverage Δ
unittests	78.14% <45.61%> (-0.13%)	⬇️

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[ekzhu]

@HariniNarasimhan checkout python/README.md for how to run auto checks locally.