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.
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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>
