PLAT-9: support alternate time dimensions

[pjain1]

Fixes https://github.com/rilldata/rill-private-issues/issues/1641

In addition to primary timeseries, another dimension of type timestamp can be specified in the list of dimensions. This dimension can be sent as request argument to aggregation, timerange, timeseries APIs and args to metrics_time_range resolver. Dimension list in the ValidSpec of the metrics view is populated with types and application can use it show alternate time dimension columns.

Note - We assume a primary time dimension will be defined in the metrics view but it can refer to any timestamp/date type from the dimension list which can have expression as well.

Checklist:

• [x] Covered by tests
• [x] Ran it and it works as intended
• [x] Reviewed the diff before requesting a review
• [x] Checked for unhandled edge cases
• [x] Linked the issues it closes
• [ ] Checked if the docs need to be updated
• [ ] Intend to cherry-pick into the release branch
• [ ] I'm proud of this work!