Add http-only warning in documentation

[alkismavridis]

related: #49495

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide (https://github.com/apache/airflow/blob/main/contributing-docs/README.rst)
Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our pre-commits will help you with that.
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[pierrejeambrun]

Nice thanks!

[alkismavridis]

@pierrejeambrun mergable seems to be stuck?

[pierrejeambrun]

@pierrejeambrun mergable seems to be stuck?

Yes, weird, lets merge it anyway

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.

[github-actions]

Backport successfully created: v3-0-test

Status	Branch	Result
✅	v3-0-test