Fix WeightRule spec

[ZhaoMJ]

Remove the enum requirement for WeightRule in OpenAPI spec, since it can be the path of the custom class when a custom weight_rule is used.

Related: #46824

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[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.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example DAG that shows how users should use it.
• Consider using Breeze environment for testing locally, it's a heavy docker but it ships with a working Airflow and a lot of integrations.
• Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
• Be sure to read the Airflow Coding style.
• Always keep your Pull Requests rebased, otherwise your build might fail due to changes not related to your commits.
  Apache Airflow is a community-driven project and together we are making it better 🚀.
  In case of doubts contact the developers at:
  Mailing List: dev@airflow.apache.org
  Slack: https://s.apache.org/airflow-slack

[pierrejeambrun]

LGTM, since this is AF2 stuff and that's not super fresh in my mind, I could use a second pair of eyes, just to confirm.

cc: @ephraimbuddy, @jedcunningham

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 5 days if no further activity occurs. Thank you for your contributions.

[Khrol]

Can I introduce some activity here with my comment? I find this PR useful because we had to patch local Airflow to use a custom weight_rule.

[pierrejeambrun]

Not sure we're going to get a new patch release for 2.11 but here it goes. (merged)

In airflow >= 3.0.0 weight_rule for Task Response object in the API is a string, so upgrading is the way to be sure that this is not a problem anymore.

[boring-cyborg]

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

[eladkal]

Not sure we're going to get a new patch release for 2.11 but here it goes. (merged)

If not mistaken @potiuk mentioned he is going to do it after #51681 is merged