Appliance Features can't be disabled once enabled

[infosec-shinobi]

ssh_server, prometheus_exporter, and healthcheck_server code blocks can't be disabled once enabled.

Problem lines:

• https://github.com/appgate/sdp-terraform-provider/blob/d9c23837c9a4ad7060573ad426aaf7e7ef9dcf6a/appgate/resource_appgate_appliance.go#L1432
• https://github.com/appgate/sdp-terraform-provider/blob/d9c23837c9a4ad7060573ad426aaf7e7ef9dcf6a/appgate/resource_appgate_appliance.go#L1459
• https://github.com/appgate/sdp-terraform-provider/blob/d9c23837c9a4ad7060573ad426aaf7e7ef9dcf6a/appgate/resource_appgate_appliance.go#L1471

"Enabled" field is being hardcoded to "true" instead of a call to the "GetEnabled" function.

PR to address coming shortly.

[dlnilsson]

Fixed in #76