SQL Expressions: Rework backend errors and error instrumentation (#109633)

* Capture error_type label on metrics/traces
* Make error messages more helpful to user
* Use errutil, categorized errors, and tie them to error_type (category in code)
* Misc trace fixes
* Add metric to track SQL input conversion

pkg/services/ngalert/eval/eval_test.go

@@ -1596,3 +1596,10 @@ func (f fakeNode) String() string {
 func (f fakeNode) NeedsVars() []string {
 	return nil
 }
+
+func (f fakeNode) IsInputTo() map[string]struct{} {
+	return nil
+}
+
+func (f fakeNode) SetInputTo(a string) {
+}