Feature Request: Experiment metrics need more aggregation types

Feature request

Is your feature request related to a problem?

In the old experiments UI, trends metrics supported more aggregation types, including SQL expression:

This allowed for more advanced calculations and use cases.

Currently, we support only a subset of those:

Describe the solution you'd like

Bring the current experiment metric aggregation types to parity with the old version, allowing users to keep making calculations on their metrics. A particular use case is calculating on data warehouse values which SQL expression allows.

Describe alternatives you've considered

• Not calculate as I was able to in the past
• Change my experiment design

Additional context

From: https://posthoghelp.zendesk.com/agent/tickets/33393 (moved to PostHog: https://us.posthog.com/project/2/support/tickets/36554)

Debug info

Kind: support

Target area: experiments

Report event: http://go/ticketByUUID/1f773e13-466e-49da-94fe-cf7153122150

Session: https://us.posthog.com/project/sTMFPsFhdP1Ssg/replay/0197bffa-9457-7e95-a748-e280e303b10c?t=1760

Exceptions: https://us.posthog.com/project/2/error_tracking?filterGroup=%7B%22type%22%3A%22AND%22%2C%22values%22%3A%5B%7B%22type%22%3A%22AND%22%2C%22values%22%3A%5B%7B%22key%22%3A%22%24session_id%22%2C%22value%22%3A%5B%220197bffa-9457-7e95-a748-e280e303b10c%22%5D%2C%22operator%22%3A%22exact%22%2C%22type%22%3A%22event%22%7D%5D%7D%5D%7D

Location: https://us.posthog.com/project/68136/experiments/shared-metrics/new

Persons-on-events mode for project: person_id_override_properties_on_events

Start at the experiments shared-metrics/new entry point referenced in the issue and compare its available aggregation types with the old experiments UI shown in the screenshots. Trace the metric calculation path and identify how SQL expression support would reach data warehouse values. The issue names no source files or tests, so locate the relevant UI and experiment metric tests first; done means parity with the old aggregation options.