Shanbady/fix course panel start date

[shanbady]

What are the relevant tickets?

Closes https://github.com/mitodl/hq/issues/5256

Description (What does it do?)

This PR sorts the date dropdown and ensures that the closest upcoming date is pre-selected in the learning resource expanded drawer

Screenshots (if appropriate):

How can this be tested?

1. checkout this branch. make sure you have data/learning resources loaded (in particular ones with multiple runs/dates)
2. find a resource with multiple upcoming runs and open the resource drawer
3. see that the dates are chronologically sorted and that the next upcoming date is preselected

[abeglova]

👍