Let users see results (and possibly create unofficial submissions) after the end of the contest

[wil93]

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

There are two problems:

1. As soon as the contest ends, we are blocking access to the list and status of submissions. This means that users cannot see the result for submissions that are sent very close to the end of the contest. This in turn leads to a series of "clarification requests" where people are asking if the last submission they just sent will be counted or not.
2. As it sometimes happens, the server is overloaded near the end of the contest since many people try to submit. This can sometimes lead to not being able to submit a solution in time.

Describe the solution you'd like

We can solve both problems:

1. By continuing to show the list and status of submissions (i.e. in read-only mode) users won't need to ask if the submission is going to be counted or not: they can simply wait and refresh the page until they see the score.
2. By letting users create new "unofficial" submissions (i.e. in read-and-write mode) we can greatly mitigate the server load issue: as soon as the contest ends, people that were not able to submit can still do it unofficially and formally request to switch their last submission to "official", and this request can be later evaluated and approved/rejected by the admins.

Describe alternatives you've considered

The most glaring alternative would be to simply start the Analysis Mode as soon as the contest ends. This would indeed solve the 2 problems listed here, however, it would also introduce unwanted features:

• During analysis mode, CMS automatically shows all execution results for the testcases (instead of respecting the "restricted mode" where only the first failing testcases are shown). This means that submissions sent after the end of the contests have more feedback from the system.
• Also, if I remember correctly, there is a concept of "hidden attachment" in CMS where some attachments are visible only during analysis mode (e.g. a PDF with the explanation of the problem or a ZIP with all the testcases).

For these reasons it would be better to implement this as a standard behavior of CMS instead of having to rely on analysis mode.

Additional context

Possibly related to #61

[fushar]

We successfully implemented this idea for IOI 2022. Relevant commits:

• ioi@5963969 (Allow contestants to view submissions after the contest ends)
• ioi@c2ade13 (Add config to allow contestants to do unofficial submissions after contest ends)