[FEATURE] Allow point values to be changed when exporting contest problems

[jdabtieu]

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

Typically, contest point values do not correspond to actual point values. As a public example, in https://dmoj.ca/contest/dmopc20c5 all problems are worth 100 points, but when exported, are worth significantly less (3-35 points). The same occurs in CTF contests - while contest questions may be worth 500 points, they are typically worth much less when exported (for MGCI CTF Club, this is 50-150 points)

Describe the solution you'd like

On the problem export page (see screenshot), there should be a field to change the point value before exporting so that they don't have to be changed after exporting.