Update from the Superset X.0 working group

[Aaron Suddjian <aa...@preset.io>]

Hi folks, the group met today to discuss the ongoing changes for Superset
2.0. Key discussion points are noted below.

- Decided to proceed with flipping the SQL_LAB_BACKEND_PERSISTENCE flag.
- Reminder that all the breaking changes need an appropriate entry in
Updating.md and that they get the appropriate PR labels, as well as a
"conventional commits" exclamation point in the title.
- Allowing two small barely-breaking changes onto the board. Future small
bycatch will be considered, subject to discussion/objection.
- Setting a merge target for March 25th, with the Celery change as the only
hard requirement.
- Will do a sweep of PRs from the board when the release branch is cut. to
make sure that all PRs have UPDATING entries and proper labeling.

Please feel free to join the next working group meeting on March 17th at
10am PST. The meeting can be found on the Superset Community Calendar.

-- 
Aaron Suddjian, Software Engineer at Preset