Simplify Zendesk driver and share time parsing

Drop the zendeskRole helper and use the raw API role, matching the other
drivers. Factor the duplicated RFC3339 timestamp parsing (parseZendeskTime
and parseDatadogTime were identical) into a shared parseRFC3339Ptr in
driver.go.

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

pkg/accessreview/drivers/driver.go

@@ -67,3 +67,19 @@ type Driver interface {
 	// ListAccounts returns all accounts from the source system.
 	ListAccounts(ctx context.Context) ([]AccountRecord, error)
 }
+
+// parseRFC3339Ptr parses an RFC 3339 timestamp into a *time.Time, returning
+// nil for an empty or unparseable value. Drivers use it for best-effort
+// timestamp fields (created_at, last_login_at) that an API may omit.
+func parseRFC3339Ptr(s string) *time.Time {
+	if s == "" {
+		return nil
+	}
+
+	t, err := time.Parse(time.RFC3339, s)
+	if err != nil {
+		return nil
+	}
+
+	return &t
+}