Create Egress Gateway range validation

[Dim0N22]

The Create Egress Gateway form requires a range and an interface. The form doesn't have any validation for ranges, so 1.2.3.4 will be accepted without any error messages even though it won't be applied in Wireguard.

There need to be validation at some level (ui / service / both).

P.S. There seems to be a regex for this, but it's unused:

netmaker-ui/src/util/regex.ts

Lines 10 to 12 in 8f73ebb

	export const correctSubnetRegex = new RegExp(
	/^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\/\d{1,3}$/i
	)