refactor(dashboards): convert dashboard templates from filters to queries

[thmsobrmlr]

Problem

We want to get rid of insights with filters eventually. All insights should use queries instead.

Currently we're still creating new insights with filters through dashboard templates.

Changes

This PR:

• adds a migration that converts existing dashboard templates from filters to queries.
• adds a flag to the filters_to_query method for supporting template variables.
• handles template variables frontend side: at the moment we only have variables for events. these need to be converted to the new entity format before sending them to the dashboard endpoint.

How did you test this code?

Loaded templates from production into my local instance and ran the migration. Tested selected dashboard templates picked by popularity and those having issues when running the migration:

• Customer Retention Rate in Test B2B SaaS Product Metrics -> variables
• product analytics (79k)
• landing pages report (4.3k)
• website metrics (3.5k)
• user research (3.5k)
• real time analytics (1.7k)

[github-actions]

Size Change: 0 B

Total Size: 1.11 MB

ℹ️ View Unchanged

Filename	Size
frontend/dist/toolbar.js	1.11 MB

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[posthog-bot]

📸 UI snapshots have been updated

1 snapshot changes in total. 0 added, 1 modified, 0 deleted:

• chromium: 0 added, 1 modified, 0 deleted (diff for shard 2)
• webkit: 0 added, 0 modified, 0 deleted

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[posthog-bot]

📸 UI snapshots have been updated

1 snapshot changes in total. 0 added, 1 modified, 0 deleted:

• chromium: 0 added, 1 modified, 0 deleted (diff for shard 2)
• webkit: 0 added, 0 modified, 0 deleted

Triggered by this commit.

👉 Review this PR's diff of snapshots.

[anirudhpillai]

Great job testing on all the prod templates!