Improve past experiment imports

[jdorn]

Features and Changes

This PR fixes a number of UX and performance issues when importing existing experiments from a data source into GrowthBook.

Changes:

• Improve labels, headers, and tooltips to be more intuitive
• Perform incremental updates when refreshing the list (with option to do a full refresh)
• On initial load, do not start the query immediately. Tell the user we are about to scan X days of data and have them confirm before starting.
• Move all filtering from the back-end to the UI and persist in localStorage to make exploration and debugging easier.
• Smarter logic for guessing variation weights, plus warn in UI that this is a guess and might be inaccurate
• Right after importing an experiment, auto-update results (opt-out toggle)

Screenshots

Note: My local IMPORT_LIMIT_DAYS variable is set to 2000 in the screenshots below. The default value is 365.

New toggle when importing to auto-run result queries on save (default ON):

[github-actions]

Your preview environment pr-2437-bttf has been deployed.

Preview environment endpoints are available at:

• https://growthbook-3000-pr-2437-bttf.growthbook.okteto.dev
• https://growthbook-3100-pr-2437-bttf.growthbook.okteto.dev

[lukesonnet]

Overall seems to work with some light QA and quick code review. Some nits were shared with you in comments.