[Feature Request]: certificate-download-modal component datepicker enhancements

[mgporter]

Is your feature request related to a problem? Please describe.

Hi all. I was working on the certificate-download-modal component for another PR, and ran across a few small issues:

1. The end date for generating the certificate is exclusive, meaning that a contribution done today will only show up if we select tomorrow as the end date.

2. The frontend datepicker allows a user to select dates in the future, however the backend server rejects dates that are in the future.

Describe the solution (or solutions) you'd like

1. It feels more natural for the end date to be inclusive, i.e., if I select May 3 as the end date for contributions, I would expect that my contributions on May 3rd would show up. We could fix this by adding one day to the user's selected end date on either the frontend or backend side of things.

2. Dates in the future should be unselectable on the frontend. Since this modal is just using an html date type input element, we can just add a max attribute to it and set that to today's date. We can keep the backend date validation check though, for extra redundancy.

Describe alternatives you've considered and rejected

No response

Additional context

If you approve of these suggestions, you can assign them to me.