SQL Expressions: Make SQL Expressions work with Alerting (#101820)

Initial support for alerting with SQL expressions

- When `format` is set to `alerting`, SQL expressions output in a format suitable for alerting evaluation.
- Outstanding TODOs:
  - Deduplicate output rows
  - Add more tests
  - Fix broken alerting UI rendering (likely due to shape change to undocumented full-long format)
- Basic usage:
  - SQL must return one numeric column and one or more string columns.
  - Each row may become an alert.
  - The alert fires if the numeric value is non-zero.
  - String columns are treated as labels.

---------

Co-authored-by: Konrad Lalik <konradlalik@gmail.com>
Co-authored-by: Tom Ratcliffe <tom.ratcliffe@grafana.com>
Co-authored-by: Sam Jewell <sam.jewell@grafana.com>

pkg/expr/reader.go

@@ -136,7 +136,7 @@ func (h *ExpressionQueryReader) ReadQuery(
 			eq.Properties = q
 			// TODO: Cascade limit from Grafana config in this (new Expression Parser) branch of the code
 			cellLimit := 0 // zero means no limit
-			eq.Command, err = NewSQLCommand(common.RefID, q.Expression, int64(cellLimit))
+			eq.Command, err = NewSQLCommand(common.RefID, q.Format, q.Expression, int64(cellLimit))
 		}
 
 	case QueryTypeThreshold: