feat: Add help text for reserving static IPs to IP mode fields MAASEN…

…G-3911 (#5550)

- Added help text about reserving IP addresses to the IP mode field in:
  - Add device
  - Add network discovery
  - Add/Edit device interface
  - Add/Edit machine interface

Resolves [MAASENG-3911](https://warthogs.atlassian.net/browse/MAASENG-3911)

src/app/base/components/IpAssignmentSelect/IpAssignmentSelect.tsx

@@ -22,6 +22,11 @@ export const IpAssignmentSelect = ({
   return (
     <FormikField
       component={Select}
+      help={
+        import.meta.env.VITE_APP_STATIC_IPS_ENABLED === "true"
+          ? "To manage static DHCP leases for a device, go to the address reservation tab of a subnet."
+          : null
+      }
       label={label}
       options={[
         { label: Labels.DefaultOption, value: "", disabled: true },

src/app/machines/views/MachineDetails/MachineNetwork/NetworkFields/NetworkFields.tsx

@@ -172,6 +172,11 @@ const NetworkFields = ({
       {values.subnet ? (
         <LinkModeSelect
           defaultOption={null}
+          help={
+            import.meta.env.VITE_APP_STATIC_IPS_ENABLED === "true"
+              ? "To manage static DHCP leases for a machine, go to the address reservation tab of a subnet."
+              : null
+          }
           interfaceType={interfaceType}
           name="mode"
           onChange={(evt: React.ChangeEvent<HTMLInputElement>) => {