DHCP NTP Options

[crawc]

Is your feature request related to existing pfSense functionality that is missing from the API? Please describe.
A URL or documentation about the requested functionality. Ex. /firewall_rule.php [...]
/services_dhcp.php?if=opt1

Is your feature request related to a problem? Please describe.
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Currently unable to set these NTP options using the API

Describe the solution you'd like
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Implement these fields when creating/updating DHCP services.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
After using the API to create the service I must use the pfSense interface (/services_dhcp.php?if=opt1) to set them and restart DHCP.

Additional context
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Great work on this! Very helpful. Please see comment from #176

Would it be possible to add the NTP servers too?
"ntpserver": [ "0.pool.ntp.org", "1.pool.ntp.org", "2.pool.ntp.org" ]