allow setting primary bond interface

[John A]

currently it is not possible to configure the "primary" parameter in netplan through the maas-ui bond configuration interface... the post linked below gives a good explanation why this setting is important: https://bugs.launchpad.net/ubuntu/+source/nplan/+bug/1709135

previously it seems that it was possible to set a primary interface from which the bond would inherit the mac address from. I am unsure if this also configured the netplan primary parameter? https://github.com/canonical/maas-ui/pull/2359

however the option above seems to have been changed in favor of the "Use MAC address from bond member" and "Manual MAC address" parameters which work as stated but it does not set the primary parameter in netplan even if you select the desired interface as the mac address for the bond. https://github.com/canonical/maas-ui/issues/2363

I think there should be an option to specify a primary interface so that it gets configured as such in netplan, or it should automatically configure the primary as the mac address provided if it matches one of the interfaces.

the documentation still references the old ui https://maas.io/docs/how-to-connect-maas-networks

[John A (johna91)]

maas report: https://bugs.launchpad.net/maas/+bug/2071864