Allow custom html template option for formly multicheckbox type

[surendranekkanti]

Is your feature request related to a problem? Please describe.
Unable to display text along with hyperlinks when using formly multicheckbox type as part of step in stepper component.

Describe the desired solution
Multicheckbox type should accept an html template so that it could be customized accordingly.

Describe alternatives you've considered
Add individual checkbox with custom template. However there are a lot of checkboxes and having them grouped and aligning them would be a problem.

Additional context
Add any other context or screenshots about the feature request here.