Register AWS VPN Client in fleet configs: add an IdP group label (IdP
group: SAML-aws-vpn), include that label in default.yml, and add
aws-vpn-client/darwin to fleet_maintained_apps (self_service=true,
labeled for the SAML-aws-vpn group). Add a dynamic label for macOS hosts
with AWS VPN Client installed (bundle id com.amazonaws.acvc.osx) and add
a macOS patch policy to surface/update hosts with out-of-date AWS VPN
Client. These changes enable inventorying, self-service installation,
and patch tracking for the AWS VPN Client.