chore: remove httpbinorg request from integration tests

[dreamorosi]

Description of your changes

As described in the linked issue, before this PR the integration tests were using httpbin.org as destination for some requests made during the Tracer tests.

This PR replaces that host with the base URL of the project's documentation to avoid reliance on 3rd party services.

How to verify this change

See test run of integration tests published in the comments below the PR.

Related issues, RFCs

Issue number: #1193

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding changes to the examples
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published
• The PR title follows the conventional commit semantics

Breaking change checklist

• I have documented the migration process
• I have added, implemented necessary warnings (if it can live side by side)

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[dreamorosi]

Passing integration test running:
https://github.com/awslabs/aws-lambda-powertools-typescript/actions/runs/3720351468/jobs/6309770023