docs: Adding limitation to TEI docs.

[drauedo]

Adding some limitations to clarify that TEI is not intended to work within the LocalStack container itself or any spawned containers by it, such as Lambda.

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[quetzalliwrites]

I think this is better now, do you agree @remotesynth?

[dfangl]

As discussed in Slack, this needs adaptions.
Copying my message here:

Transparent endpoint injection is a combination of us redirecting requests using DNS, and of us disabling certificate validation for these requests (because otherwise, something will complain if using https). The DNS part works in both the LocalStack container itself, and the spawned compute containers. The certificate part only works for processes we control ourselves, so usually Lambda (managed runtimes) and processes we ourselves start in the LocalStack container. This is why the customer reported the issue - the request was redirected correctly, but we did not disable certificate validation.
Taking this in mind, I think it is worth adding a warning in the docs, that while the DNS redirects the requests both inside the main LS container, and the spawned containers, they might run into certificate issues they have to resolve themselves. (Or use AWS_ENDPOINT_URL as a better alternative, if their SDK is new enough).

[remotesynth]

@dfangl Sorry for the slow response here. I attempted to address this change request by adding another bullet point, though the details were a bit difficult to explain clearly. Please let me know if the following bullet point would address the changes requested:

- Transparent endpoint injection involves a combination redirecting requests using DNS and disabling certificate validation for these requests (to avoid issues when using https). Disabling certificate validation only works for processes LocalStack controls, for example Lambda (managed runtimes) and processes LocalStack starts within the LocalStack container. This means that, even whein cases where DNS properly redirects the requests both inside the main LocalStack container and any spawned containers, you may still encounter certificate issues for processes not spawned directly by LocalStack. To avoid this issue, use `AWS_ENDPOINT_URL=http://localhost.localstack.cloud:4566` as an alternative.

[dfangl]

Thanks for adding the additional paragraph! I added some more suggestions, feel free to rephrase them if necessary, then we can merge 🎉