migration(issue-views): Make groupsearchview.position nullable

[MichaelSun48]

This PR makes the groupsearchview.position column nullable. This is the first step to deleting the column entirely, since it's being superseded by the groupsearchviewstarred.position column.

The next steps after merging this are:

1. Delete all usages of this column — Besides tests, there are already no more places where we are filtering based on the position, but we need to remove the position from any newly created entries.
2. Add migration to safe delete the column w/ pending deletion_action=DeletionAction.MOVE_TO_PENDING
3. Add migration to fully delete the column

^ If these steps are incorrect, please let me know. The migration docs seem to be a little unclear about this.

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/0843_make_groupsearchview_postition_nullable_for_deletion.py ()

--
-- Alter field position on groupsearchview
--
ALTER TABLE "sentry_groupsearchview" ALTER COLUMN "position" DROP NOT NULL;

[markstory]

Schema change looks good.

[markstory]

If these steps are incorrect, please let me know. The migration docs seem to be a little unclear about this.

Those are the correct steps 👍