Add support for custom celery configs

[arorasachin9]

closes: https://github.com/apache/airflow/issues/45037

Description: Currently Airflow support limited celery options only. This PR adds the support for the additional celery config for celery workers.

1. Changes are completely backward compatible
2. No test cases found for these changes
3. If the config is not available then default value of {} is taken which will be same as earlier only
4. If config is available then it will be added to the celery config and applied to celery workers.

[boring-cyborg[bot]]

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[arorasachin9]

Addressed the comments. CI is failing not able to debug why CI pipeline is failing.

[jscheffl]

Except some minor comment I think it is good, let me check what is broken on CI. Nothing related to your code. Ignore that it is "red" atm, will be better once you push the next change on the PR.

Then I think... LGTM!

[jscheffl]

Somthing is wrong with this PR and CI - I don't see the reason but I am very sure it is not related to the changes. I am on it...

[arorasachin9]

@jscheffl I have fixed the unit test. The CI is passing. and Thanks for the help in dubuging the CI issue.

[boring-cyborg[bot]]

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