Create tasks to replace generate_* management commands

[jennifer-richards]

Description

Need to create Celery tasks to replace the following management commands

• ietf/doc/management/commands/generate_idnits2_rfc_status.py
• ietf/doc/management/commands/generate_idnits2_rfcs_obsoleted.py
• ietf/doc/management/commands/generate_draft_bibxml_files.py

The last of these has options that I believe are not used, so it would be fine if it assumes the default for all options (though it wouldn't hurt to keep them as arguments to the task).

We should keep the management commands around for now, we will remove them once we've switched to the task-based implementations.

Code of Conduct

• I agree to follow the IETF's Code of Conduct