SQL Expressions: Enable Auto-complete (#106511)

* First draft autocomplete

* Better naming

* Change suggestion to table/column population

* Remove all suggestions, just use table/column population but trigger on space

* Gate feature flag behind a feature flag

* Reorganize and add function list

* Add blurb about autocomplete to docs

* Update public/app/features/expressions/utils/metaSqlExpr.ts

Co-authored-by: Alex Spencer <52186778+alexjonspencer1@users.noreply.github.com>

* Add try catch, remove promise resolve

---------

Co-authored-by: Alex Spencer <52186778+alexjonspencer1@users.noreply.github.com>

pkg/services/featuremgmt/registry.go

@@ -803,6 +803,13 @@ var (
 			FrontendOnly: false,
 			Owner:        grafanaDatasourcesCoreServicesSquad,
 		},
+		{
+			Name:         "sqlExpressionsColumnAutoComplete",
+			Description:  "Enables column autocomplete for SQL Expressions",
+			Stage:        FeatureStageExperimental,
+			FrontendOnly: true,
+			Owner:        grafanaDataProSquad,
+		},
 		{
 			Name:         "groupToNestedTableTransformation",
 			Description:  "Enables the group to nested table transformation",