Mv rows export

[pjain1]

Fixes https://github.com/rilldata/rill-private-issues/issues/1342

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• 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!

[begelundmuller]

1. Also needs to update the MetricsViewRows RPC to use the metricsview package (to fix the original bug)
2. Can you also add some tests in runtime/resolvers/testdata for the rows logic? Especially to check the measure filter support that was originally reported. I.e. have tests like:

...
tests:
- name: metrics rows with a measure-based filter
  resolver: metrics
  properties:
    metrics_view: foo
    rows: true
    ...

[pjain1]

Also needs to update the MetricsViewRows RPC to use the metricsview package (to fix the original bug)

I thought UI can switch to mv agg API and we can deprecate rows API

[pjain1]

metricsview_rows export marshals values before writing like

func convertToXLSXValue(pbvalue *structpb.Value) (interface{}, error) {
	switch pbvalue.GetKind().(type) {
	case *structpb.Value_StructValue:
		bts, err := protojson.Marshal(pbvalue)
		if err != nil {
			return "", err
		}

		return string(bts), nil
	case *structpb.Value_NullValue:
		return "", nil
	default:
		return pbvalue.AsInterface(), nil
	}
}

however mv agg export does not thats why the date format is of excel format.