128 workflow cleanup

Created by: ri-pandey

Description

1. Purge workflows from Celery persistence that have been unavailable in the app's state (i.e. in relational db) for more than 24 hours.
2. Purge tasks (which belong to this instance of Bioloop) from Celery persistence whose associated workflows have been unavailable in the app's state (i.e. in relational db) for more than 24 hours.

Related Issue(s)

Closes #128 (closed)

Changes Made

List the main changes made in this PR. Be as specific as possible.

• Feature added
• Other changes: [describe]
• added cron schedule which runs the script twice a week (Mondays and Wednesdays)

Checklist

Before submitting this PR, please make sure that:

• Your code passes linting and coding style checks.
• Documentation has been updated to reflect the changes.
• You have reviewed your own code and resolved any merge conflicts.
• You have requested a review from at least one team member.
• Any relevant issue(s) have been linked to this PR.