Remove email configs, operator and callbacks

[hussein-awala]

This PR:

• removes the ability to use email_on_retry and email_on_failure to notify the users by email in favor of the SMTP notifier
• removes EmailOperator from airflow.operators.email in favor of airflow.providers.smtp.operators.smtp.EmailOperator
• cleans their usage and remove SMTP section from Airflow configuration

closes: #30530

[hussein-awala]

      - id: check-no-providers-in-core-examples
        language: pygrep
        name: No providers imports in core example DAGs
        description: The core example DAGs have no dependencies other than standard provider or core Airflow
        entry: "^\\s*from airflow\\.providers.(?!standard.)"
        pass_filenames: true
        files: ^airflow/example_dags/.*\.py$

What about pre-installed providers? if we really want to keep the rule as it is, then I will need to update the example.

[eladkal]

I don't think we should do that. We should keep pre-installed to the minimum necessary.
Probably raise this as one of the items in the lazy consensus

[eladkal]

We need also to remove the email and smtp part of airflow.cfg
https://airflow.apache.org/docs/apache-airflow/stable/configurations-ref.html#email

https://airflow.apache.org/docs/apache-airflow/stable/configurations-ref.html#smtp

[eladkal]

I merged #47146
@hussein-awala what is left to be completed on this PR?

[uranusjr]

Do we still want to do this? Happy to help if so.

[eladkal]

Do we still want to do this? Happy to help if so.

Yes. we need to sort this one out before RC1

[uranusjr]

We never did anything, and now 3.0 is out…

What do we do next?

[eladkal]

We never did anything, and now 3.0 is out…

What do we do next?

Move the email util from airflow-core to smtp provider with airflow4 deprecation warning.
Deprecate email configs from core in favor smtp configs

[uranusjr]

We actually already made some changes and deprecated some configs during task sdk implementation. I think this needs to start from scratch. I’m going to do some of the config changes to catch up with task sdk changes first.

[github-actions]

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[zachliu]

We need also to remove the email and smtp part of airflow.cfg

hooray! this surely simplifies things a lot!