fix(localstack/lambda): lambda debugging

[skyrpex]

Problem

The AWS SDK v2 to v3 migration in PR #8183 introduced breaking changes for LocalStack compatibility and Lambda debugging is not working anymore:

1. User Agent format changed: The migration changed from string-based user agents to AWS SDK v3's UserAgent pairs format ([name, version] tuples), but several places still used the old string format, breaking LocalStack's custom user agent for Lambda debugging
2. Response headers no longer accessible: AWS SDK v3 removed access to HTTP response headers via $response.httpResponse.headers, breaking LocalStack connection detection which relies on the x-localstack-request-url header

These issues were not caught most likely because LocalStack compatibility was not tested during the SDK v3 migration.

Solution

1. Add response headers middleware for AWS SDK v3

   • Added captureHeadersMiddleware to AWSClientBuilderV3 that attaches HTTP response headers to the output via $httpHeaders property
   • Updated loginManager to check for LocalStack connection using $httpHeaders instead of the removed $response.httpResponse.headers

2. Fix user agent format for AWS SDK v3

   • Migrated from string-based user agents to proper UserAgent pairs format:
     • Changed from "LAMBDA-DEBUG/1.0.0 AWS-Toolkit/..." (string)
     • To [['LAMBDA-DEBUG', '1.0.0'], ['AWS-Toolkit', '2.0'], ...] (pairs)
   • Updated awsClientBuilderV3 to use customUserAgent instead of userAgent

AWS SDK v3 Breaking Changes

User Agent Format

SDK v2:

// String format in client options
const options = {
    region: 'us-east-1',
    userAgent: 'LAMBDA-DEBUG/1.0.0 AWS-Toolkit/2.0.0'
}

SDK v3:

// Array of [name, version] tuples
const options = {
    region: 'us-east-1',
    customUserAgent: [
        ['LAMBDA-DEBUG', '1.0.0'],
        ['AWS-Toolkit', '2.0.0']
    ]
}

Response Headers Access

SDK v2:

const response = await client.send(command)
// Headers directly accessible
const headers = response.$response.httpResponse.headers
const localStackUrl = headers['x-localstack-request-url']

SDK v3:

const response = await client.send(command)
// Headers NOT accessible by default - requires custom middleware
const headers = response.$httpHeaders  // undefined without middleware

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Supersedes #8289 as @carole-lavillonniere is OOO today and can't edit their PR.