SQL Expressions: Add sql expression specific timeout and output limit (#104834)

Adds settings for SQL expressions:
 sql_expression_cell_output_limit

Set the maximum number of cells that can be returned from a SQL expression. Default is 100000.

sql_expression_timeout

The duration a SQL expression will run before being cancelled. The default is 10s.

pkg/setting/setting.go

@@ -428,6 +428,12 @@ type Cfg struct {
 	// SQLExpressionCellLimit is the maximum number of cells (rows × columns, across all frames) that can be accepted by a SQL expression.
 	SQLExpressionCellLimit int64
 
+	// SQLExpressionOutputCellLimit is the maximum number of cells (rows × columns) that can be outputted by a SQL expression.
+	SQLExpressionOutputCellLimit int64
+
+	// SQLExpressionTimeoutSeconds is the duration a SQL expression will run before timing out
+	SQLExpressionTimeout time.Duration
+
 	ImageUploadProvider string
 
 	// LiveMaxConnections is a maximum number of WebSocket connections to
@@ -800,6 +806,8 @@ func (cfg *Cfg) readExpressionsSettings() {
 	expressions := cfg.Raw.Section("expressions")
 	cfg.ExpressionsEnabled = expressions.Key("enabled").MustBool(true)
 	cfg.SQLExpressionCellLimit = expressions.Key("sql_expression_cell_limit").MustInt64(100000)
+	cfg.SQLExpressionOutputCellLimit = expressions.Key("sql_expression_output_cell_limit").MustInt64(100000)
+	cfg.SQLExpressionTimeout = expressions.Key("sql_expression_timeout").MustDuration(time.Second * 10)
 }
 
 type AnnotationCleanupSettings struct {