Error should be exposed in balenaDashboard when you set an invalid configuration value

Hi,

I had to open up a support ticket because I had accidentally set an invalid character in the dtparam value for one of my machines. My device stopped taking variable/config changes after I added the invalid value but I didn’t know what was going on.

It would be nice to do some validation of the values and then expose any formatting errors in balenaDashboard.

Ticket #6387