Add Grafana access review connector support

Add Grafana as an access review connector-backed source.

This introduces a Grafana access-review driver, provider registration,
and connector settings for the Grafana base URL. It also wires the
new provider through GraphQL and access-review UI input mapping so
API-key connectors can be created from the product.

A connector_provider enum migration is included so Grafana can be
persisted in existing databases.

Signed-off-by: Cursor Agent <cursoragent@cursor.com>

Co-authored-by: Bryan FRIMIN <bryan@frimin.fr>

pkg/connector/provider/builtin.go

@@ -30,6 +30,7 @@ func NewBuiltinRegistry() *Registry {
 		cloudflareRegistration(),
 		cursorRegistration(),
 		docusignRegistration(),
+		grafanaRegistration(),
 		githubRegistration(),
 		gitlabRegistration(),
 		googleWorkspaceRegistration(),