Various updates to task management

[jleaniz]

Description of the change

This PR

• Fixes an issue in which task status is not properly tracked, which caused request status to never fully complete.
• Adds a result_backend configuration option for Celery in order to persist celery task metadata in Redis.
• Adds a worker_deduplicate_successful_tasks configuration option to Celery to avoid duplicate messages of successful tasks.
• Adds a task_reject_on_worker_lost configuration option to Celery so tasks can be re-queued if a worker abruptly exists (e.g. SIGTERM/SIGKILL signal sent from GKE or OS process to celery worker)
• Adds a celery_id attribute to Turbinia tasks for traceability between Turbinia and Celery tasks.
• Enables Celery mingle in the configuration to be able to handle revoked tasks between workers and worker clock synchronization.
• adds some additional exception handling when queueing tasks.
• adds some minor UI enhancements.

Applicable issues

• fixes [Bug]: Web UI large request completion percentage incorrect #1556
• fixes an issue with task state tracking

Additional information

Checklist

• All tests were successful.
• Unit tests added.
• Documentation updated.

[aarontp]

Just a couple comments, but as discussed I can potentially work on these in a separate PR.

[aarontp]

LGTM