issue 45114: Allow SMTP user and password to be set from airflow.cfg

[Mamiololo01]

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Closes: #45114

[boring-cyborg]

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[eladkal]

There will be no option to define smtp in airflow.cfg after #30531 is completed.

@hussein-awala has plans to refacor this area of the code

[Mamiololo01]

@eladkal noted and thanks for the info.