Chore: Define promlib depguard rules (#85082)

* define promlib depguard rules

* add comment

* test: break linting on purpose

* fix linting

* simple change to trigger backend linting/build in CI pipeline

.golangci.toml

@@ -67,6 +67,19 @@ files = [
   "**/pkg/tsdb/cloudwatch/**/*",
 ]
 
+[linters-settings.depguard.rules.promlib]
+list-mode = "lax" # allow unless explicitely denied
+deny = [
+  { pkg = "github.com/grafana/grafana/pkg", desc = "promlib is not allowed to import grafana core" }
+]
+allow = [
+  "github.com/grafana/grafana/pkg/promlib"
+]
+files = [
+  "**/pkg/promlib/*",
+  "**/pkg/promlib/**/*"
+]
+
 [linters-settings.gocritic]
 enabled-checks = ["ruleguard"]
 [linters-settings.gocritic.settings.ruleguard]

pkg/promlib/healthcheck_test.go

@@ -36,7 +36,7 @@ func (rt *healthCheckSuccessRoundTripper) RoundTrip(req *http.Request) (*http.Re
 				"resultType": "scalar",
 				"result": [
 					1692969348.331,
-					"2"
+					"3"
 				]
 			}
 		}`)),