Add Zendesk access-review connector

Zendesk is a multi-tenant OAuth connector keyed by the customer
subdomain. The customer enters it at connect time; it rides the signed
state to the callback, is re-validated, and is stored on the connector
settings to build the API host.

List staff (agents and admins) via GET /api/v2/users.json with cursor
pagination, mapping role, active/suspended, and 2FA status; end-users
are excluded. The subdomain is validated as a single DNS label at every
trust boundary to close the SSRF vector, and the data client keeps the
SSRF-protected transport.

Zendesk OAuth across customer subdomains requires a Zendesk-approved
global OAuth client; the connector goes live once those credentials are
supplied via bootstrap.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/coredata/connector_settings.go

@@ -122,6 +122,16 @@ type (
 	OktaConnectorSettings struct {
 		Domain string `json:"domain"`
 	}
+
+	// ZendeskConnectorSettings holds the per-customer Zendesk subdomain
+	// captured at connect time (the customer types it before the OAuth
+	// redirect, and it rides the signed state token to the callback —
+	// Zendesk does not echo it back). Subdomain is the <subdomain> part of
+	// <subdomain>.zendesk.com, used by the driver to build the API host and
+	// by the name resolver for the AccessSource title.
+	ZendeskConnectorSettings struct {
+		Subdomain string `json:"subdomain"`
+	}
 )
 
 // GrantType returns the OAuth2 grant type recorded on the connector's