Alerting: Move templating to template package (#63347)

This commit moves templating from the state package to a sub-package
called template. This sub-package will be the logical package for
future ease-of-use improvements to templating custom annotations
and labels.

pkg/services/ngalert/state/template/funcs.go

@@ -0,0 +1,41 @@
+package template
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/url"
+	"text/template"
+)
+
+type query struct {
+	Datasource string `json:"datasource"`
+	Expr       string `json:"expr"`
+}
+
+var (
+	defaultFuncs = template.FuncMap{
+		"graphLink": graphLink,
+		"tableLink": tableLink,
+	}
+)
+
+var (
+	graphLink = func(data string) string {
+		var q query
+		if err := json.Unmarshal([]byte(data), &q); err != nil {
+			return ""
+		}
+		datasource := url.QueryEscape(q.Datasource)
+		expr := url.QueryEscape(q.Expr)
+		return fmt.Sprintf(`/explore?left={"datasource":%[1]q,"queries":[{"datasource":%[1]q,"expr":%q,"instant":false,"range":true,"refId":"A"}],"range":{"from":"now-1h","to":"now"}}`, datasource, expr)
+	}
+	tableLink = func(data string) string {
+		var q query
+		if err := json.Unmarshal([]byte(data), &q); err != nil {
+			return ""
+		}
+		datasource := url.QueryEscape(q.Datasource)
+		expr := url.QueryEscape(q.Expr)
+		return fmt.Sprintf(`/explore?left={"datasource":%[1]q,"queries":[{"datasource":%[1]q,"expr":%q,"instant":true,"range":false,"refId":"A"}],"range":{"from":"now-1h","to":"now"}}`, datasource, expr)
+	}
+)