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/query.request.example.json

@@ -13,8 +13,8 @@
       "refId": "B",
       "maxDataPoints": 1000,
       "intervalMs": 5,
-      "type": "math",
-      "expression": "$A - $B"
+      "expression": "$A - $B",
+      "type": "math"
     },
     {
       "refId": "C",
@@ -31,11 +31,11 @@
       "refId": "D",
       "maxDataPoints": 1000,
       "intervalMs": 5,
-      "upsampler": "pad",
-      "type": "resample",
+      "downsampler": "last",
       "expression": "$A",
-      "window": "1d",
-      "downsampler": "last"
+      "type": "resample",
+      "upsampler": "pad",
+      "window": "1d"
     },
     {
       "refId": "E",
@@ -68,7 +68,6 @@
       "refId": "F",
       "maxDataPoints": 1000,
       "intervalMs": 5,
-      "expression": "A",
       "conditions": [
         {
           "evaluator": {
@@ -79,13 +78,13 @@
           }
         }
       ],
+      "expression": "A",
       "type": "threshold"
     },
     {
       "refId": "G",
       "maxDataPoints": 1000,
       "intervalMs": 5,
-      "expression": "B",
       "conditions": [
         {
           "evaluator": {
@@ -134,6 +133,7 @@
           }
         }
       ],
+      "expression": "B",
       "type": "threshold"
     },
     {
@@ -141,6 +141,7 @@
       "maxDataPoints": 1000,
       "intervalMs": 5,
       "expression": "SELECT * FROM A limit 1",
+      "format": "",
       "type": "sql"
     }
   ]