Fix celery visibility timeout (set to 23.5h instead of the intended 24h)

[seanmuth]

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PR #40879 was intended to increase the default for the Celery provider's visibility_timeout from 6h to 24h, which is set in seconds. A simple reversal of numbers inadvertently set it to 84600s (23.5h) instead of 86400 (24h)

This PR corrects that, as well as adds a default value for visibility_timeout in celery's provider.yaml file so sphinx picks it up and includes that in the docs page, which currently shows there is no default (there is)

[boring-cyborg]

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[seanmuth]

cc @ephraimbuddy since yours was the original PR

[boring-cyborg]

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