[AWS Firehose quickstart] Port 4433 to serverless docs

[alaudazzi]

Description

Port https://github.com/elastic/observability-docs/pull/4433 to serverless docs.

Documentation sets edited in this PR

Check all that apply.

• [ ] Stateful (docs/en/observability/*)
• [X] Serverless (docs/en/serverless/*)
• [ ] Integrations Developer Guide (docs/en/integrations/*)
• [ ] None of the above

Related issue

Closes https://github.com/elastic/observability-docs/issues/4434

Checklist

• [X] Product/Engineering Review
• [ ] Writer Review

Follow-up tasks

Select one.

• This PR does not need to be ported to another doc set because:
  • [X] The concepts in this PR only apply to one doc set (serverless or stateful)
  • [ ] The PR contains edits to both doc sets (serverless and stateful)
• This PR needs to be ported to another doc set:
  • [ ] Port to stateful docs: \
  • [ ] Port to serverless docs: \

[github-actions[bot]]

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[alaudazzi]

@mykolaharmash Can you have a look and confirm the text is OK for serverless?