fix(mcp_proxy_for_aws/utils.py): add override for bedrock-agentcore service name detection

[arangatang]

Fixes failures when connecting to an Agentcore service.

Summary

Bedrock AgentCore url structure does not align to our current --service detection regex. For now i'm adding an override if we realize we will need more overrides as time goes on we should re-evaluate the regex itself.

Changes

Adding a check for .bedrock-agentcore. in the url and using this as service if found.

User experience

After fix users connecting to AgentCore can omit the --service flag.

Checklist

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• I have reviewed the contributing guidelines
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Is this a breaking change? (Y/N)

• Yes
• No

Please add details about how this change was tested.

• Did integration tests succeed?
• If the feature is a new use case, is it necessary to add a new integration test case?

Acknowledgment

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[arangatang]

Should fix #78

[harv-aws]

Aligned on functionality. added a minor comment on test.