Add width property to MultiSelectDropDown and make the default width fit the content of the placeholder text

[Duncanr-glitch]

Is your feature request related to a problem? Please describe.
To make the dropdown's width by default fit the place holder's text

Describe the solution you'd like
While achieving the above, it is best applied by adding that as the default width through an explicit width property on the multiselect dropdown

Describe alternatives you've considered
NA

I am considering making a PR for this issue
Yes, right away

[s-cork]

see the reference docs:
https://developer.snapappointments.com/bootstrap-select/examples/#width

I think the default should probably be "auto"
and "fit" should be documented.

I think we can just use the API provided to us by the javascript library rather than writing our own.

Thoughts?