Add trust center base domain configuration

Introduce the trust center base domain setting (default probopage.com)
so managed default domains can be minted for every compliance page.
This configuration is a prerequisite for the domain-ownership migration
and the default-domain provisioning that happens at organization
creation.

Signed-off-by: Bryan Frimin <bryan@probo.com>

pkg/probodconfig/config.go

@@ -83,6 +83,7 @@ type (
 	TrustCenterConfig struct {
 		HTTPAddr      string              `json:"http-addr,omitempty"`
 		HTTPSAddr     string              `json:"https-addr,omitempty"`
+		BaseDomain    string              `json:"base-domain,omitempty"`
 		ProxyProtocol ProxyProtocolConfig `json:"proxy-protocol,omitzero"`
 	}
 )