Use freeze time to calculate value of dynamic challenge

[Typhlos]

Solves #2320

I used the code used in the scoreboard to edit the function calculate_value and filter the solves using freeze time and only keep the solves before freeze time.

Let me know if there is anything missing.

[ColdHeat]

I think this leads to the inverse of the original problem. For example if we freeze time and then the event continues to run, if we then unfreeze the challenge values will be the frozen values until their next recalculation.

[codecov]

Codecov Report

Merging #2322 (b815af1) into master (23cdf85) will decrease coverage by 0.08%.
The diff coverage is 57.14%.

❗ Current head b815af1 differs from pull request most recent head d2635dc. Consider uploading reports for the commit d2635dc to get more accurate results

@@            Coverage Diff             @@
##           master    #2322      +/-   ##
==========================================
- Coverage   87.56%   87.48%   -0.08%     
==========================================
  Files         146      146              
  Lines        8899     8919      +20     
==========================================
+ Hits         7792     7803      +11     
- Misses       1107     1116       +9     

Impacted Files	Coverage Δ
CTFd/utils/challenges/__init__.py	91.42% <33.33%> (-8.58%)	⬇️
CTFd/api/v1/config.py	95.83% <60.00%> (-1.10%)	⬇️
CTFd/plugins/dynamic_challenges/__init__.py	97.01% <85.71%> (-1.35%)	⬇️

... and 1 file with indirect coverage changes

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[Typhlos]

I'll try to see if it's not possible to recalculate all values on unfreeze.

And I'll fix the linting

[Typhlos]

@ColdHeat I modified the code so that on any modification of freeze time, all values are recalculated

[Typhlos]

@ColdHeat please tell me if there's anything missing in the PR

[ColdHeat]

Instead of having a special case on freeze, I think a better strategy would be to have a list of plugin functions that will be called when config is updated. This way the dynamic value plugin (or other plugins) can register a function to be called after config is updated.