Add Notifiers to provider information

[eladkal]

Body

Similar to #29918

We have notifiers exposed in provider info but no mechanism to expose them.

• add notifications to provider.yaml schema (verify that all current notifiers in code base presented in provider.yaml) Add discoverability for triggers in provider.yaml #31576
• add notifications to provider_info schema
• expose notifications via Providers Manager
• add CLI notifications command to airflow providers add CLI notification commands to providers #33116
• add automated exposure of notifications in the docs (needs to be exposed at list of notifiers in airflow docs and as part of the provider index)
• check notifications classes are present in provider.yaml in unit tests Improve provider verification pre-commit #33640

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.

[omidroshani]

I'm interested in collaborating on it. Could you please let me know if I can work on this issue?

[potiuk]

I'm interested in collaborating on it. Could you please let me know if I can work on this issue?

Feel free.

[okirialbert]

I'd like to collaborate on this issue.

[potiuk]

Assigned you both. Check with @omidroshani what's the status please.

[potiuk]

CC: @eladkal - also checked "add notifications to provider_info schema. It is already there.