refactor(insights): add migration to convert filters to query

[thmsobrmlr]

Problem

We're currently migrating insight filters to query in Django shell. Unfortunately self-hosted users are left out.

Changes

Does the same for self hosted users.

⚠️ This should only be merged after we completed the migration with Django shell. ⚠️

How did you test this code?

DEBUG=1 python manage.py migrate
DEBUG=1 python manage.py migrate posthog 0458_alter_insightviewed_team_alter_insightviewed_user

SELECT COUNT(filters->>'migrated_at') * 1.0 / COUNT(*) FROM posthog_dashboarditem

[skoob13]

It looks great! It only needs to update the migration number;

[posthog-bot]

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