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/sql_command_test.go

@@ -15,7 +15,7 @@ import (
 )
 
 func TestNewCommand(t *testing.T) {
-	cmd, err := NewSQLCommand("a", "select a from foo, bar", 0)
+	cmd, err := NewSQLCommand("a", "", "select a from foo, bar", 0)
 	if err != nil && strings.Contains(err.Error(), "feature is not enabled") {
 		return
 	}
@@ -123,7 +123,7 @@ func TestSQLCommandCellLimits(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			cmd, err := NewSQLCommand("a", "select a from foo, bar", tt.limit)
+			cmd, err := NewSQLCommand("a", "", "select a from foo, bar", tt.limit)
 			require.NoError(t, err, "Failed to create SQL command")
 
 			vars := mathexp.Vars{}