[Feature Request] Allow setting "option dhcp-option-overload" in DHCP web gui

[matthawkins90]

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• I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
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Is your feature request related to a problem? Please describe.

In order to allow unifi flex mini switches (which cannot be ssh-ed into) to be adopted by a unifi controller on a different subnet, I need to set DHCP Option 43 to point to the IP address of the unifi controller. Following this guide, I tried various ways of inputting the value 01:04:<hex-encoded-ip-address>. Finally, the method that "looked correct" after packed inspection was to use Type: String and 01:04:<hex-encoded-ip-address> without being surrounded by quotation marks. However, even though it looked correct in the packet inspection, it still won't work, and my unifi switches continue to remain undiscovered. This opnsense forum post suggests that I set the option dhcp-option-overload. However, I really have no idea how to do that, even after ssh-ing into opnsense.

Describe the solution you like

I would like to be able to modify the option dhcp-option-overload value from within the web gui.

Describe alternatives you considered

I tried ssh-ing into the router to modify /var/dhcpd/etc/dhcpd.conf, but it didn't work and my changes got reset after I restarted dhcpd.

[AdSchellevis]

rfc suggests code 53 (https://datatracker.ietf.org/doc/html/rfc2132#section-9.3)