Added a select all feature

[Nathan-Roberts123]

What issue does this pull request resolve?
This will pull request will add a new feature that was requested by users, this feature allows a user to click on a select all button to select all options in a multiple select input. Issue #821

What changes did you make?
I added a button to select all options in a multiple input options menu, and I created the function to handle that click and add all options to selectedOptions array. I also wrote a test for the feature.

Is there anything that requires more attention while reviewing?
No, I don't think there is.

[Nathan-Roberts123]

The feature looks something like this.

[namti]

Any updates of this pull request? Would be great if this feature is considered.

[ericgio]

@namti Unlikely that I will add this specific feature since the functionality is already possible via a workaround. In general, I'm trying to avoid one-off features or solutions that don't scale for other use cases. I should actually look into generalizing the pagination option to allow for any kind of custom item + behavior.