Add filters to Dolos integration in Radar

[mikaelGusse]

Description

What?

Add filters to Dolos integration to allow the user to only send one submission per student or even just flagged submissions.

Why?

This should considerably speed up report generation and report readability.

How?

Changed Radar+Dolos UI with a select box which allows the user to select a filter mode. Added more functions to the Exercise model to allow for returning different sets of submissions.

Fixes #

Testing

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What type of test did you run?

• Accessibility test using the WAVE extension.
• Django unit tests.
• Selenium tests.
• Other test. (Add a description below)
• Manual testing.

[ADD A DESCRIPTION ABOUT WHAT YOU TESTED MANUALLY]

Did you test the changes in

• Chrome
• Firefox
• This pull request cannot be tested in the browser.

Think of what is affected by these changes and could become broken

Translation

• Did you modify or add new strings in the user interface? (Read about how to create translation)

Programming style

• Did you follow our style guides?
• Did you use Python type hinting in all functions that you added or edited? (type hints for function parameters and return values)

Have you updated the README or other relevant documentation?

• documents inside the doc directory.
• README.md.
• Aplus Manual.
• Other documentation (mention below which documentation).

Is it Done?

• Reviewer has finished the code review
• After the review, the developer has made changes accordingly
• Customer/Teacher has accepted the implementation of the feature

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