feat(s3): aws s3 source - add request payer support

[vibe]

Summary

Adds a request_payer option to the aws_s3 source. When set to requester, Vector includes the request payer on S3 GetObject calls so it can read objects from Requester Pays buckets.

Leaving the option unset keeps the current behavior.

This also includes the generated config docs, example configuration, tests, and a changelog update.

Vector configuration

sources:
  s3:
    type: aws_s3
    region: us-east-1
    request_payer: requester
    sqs:
      queue_url: https://sqs.us-east-1.amazonaws.com/123456789012/my-queue

How did you test this PR?

Tested locally.

Commands run:

cargo test --lib --no-default-features --features sources-aws_s3 sources::aws_s3
make check-fmt
make check-markdown
make check-changelog-fragments
make generate-docs
VECTOR_BIN=target/debug/vector make -C website validate-config-examples

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines (https://github.com/vectordotdev/vector/blob/master/changelog.d/README.md).
• No. A maintainer will apply the no-changelog label to this PR.

References

• Closes: S3 Request Payer support #26026

---

I guess on another note, I'm happy to expand the tests, but felt mocking to test the underlying conversion of the passed in option -> aws header....seemed a bit overkill and not our responsibility.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[vibe]

I have read the CLA Document and I hereby sign the CLA.

[vibe]

recheck