Update pickadate.d.ts typing for container option

Pickadate.js allows for the container option to be either a selector string
or DOM element. The latter is useful in many situations. See this line in the source:
https://github.com/amsul/pickadate.js/blob/dev/lib/picker.js#L119
Merge pull request #2952 from adidahiya/pickadate

Update pickadate.d.ts typing for container option