test(lambda): remote debugging user-agent test

[roger-zhangg]

Problem

We removed the test in :https://github.com/aws/aws-toolkit-vscode/pull/8318/files
due to localproxy not mocked correctly.

Solution

Fixed the issue and now adding back these tests.
This test starts a mock server and captures the actual user-agent being sent to make sure we are sending correct UA.

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