feat(experiments): Use a HogQL expression data warehouse setup

[danielbachhuber]

See #26332

Changes

Adds the ability to use a HogQL expression for the Distinct ID or Timestamp when setting up a data warehouse table as an experiment metric:

Also abstracts <HogQLDropdown> to a reusable component.

The backend logic doesn't quite work yet: https://posthog.slack.com/archives/C019RAX2XBN/p1733332418425019

How did you test this code?

• Selected "HogQL Expression" and verified the component displayed as expected.
• Clicked on the component, added an expression, and verified it appeared as expected.
• Saved the configuration, re-opened it, and verified the expression was still in place.
• Verified I could select a non-HogQL expression too.

[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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[andehen]

looks good from a newbie's bird perspective 👍