allow "typeaheadDebounceInterval" on material select fields to be set via templateOptions

[stephenatchison]

First of all we think Formly is great (been using it since AngularJs - thank you for all your work.

Is your feature request related to a problem? Please describe.
We are using Formly with the Material components and need to set the debounce time on select fields so that more than one character can be used to search for an entry. We haven't found a way to do this yet. If the debounce time is not set only the first letter of each entry will be considered.

Describe the solution you'd like
Ideally we would like to be able to set the debounce time using a templateOptions property.

Describe alternatives you've considered
We considered using a wrapper, but couldn't get access to the mat-select component itself. We alse considered copying the formly material select component and extending it with the required templateOption.