Merge updates from 2023 CommNet lecture.

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For this iteration, we did a lot of small updates, mainly:

• the matrix container can now be controlled via docker pause and docker unpause.
• the matrix also returns timestamps of when it last ran, and the website can show this appropriately.
• the matrix frequency can now be more easily controlled with environment variables.
• the generate_configs.py script was reworked to change topology sizes more easily.
• support for new permanent hijacks (optional) between stub ASe. These allow testing RPKI without global hijacks affecting everyone).
• A few small fixes and improvements here and there.

@KTrel , I tested the basic setup to make sure everything can be set up without issues, and it seems to work for me.
But I'd be thankful if you could try setting the default configuration up yourself and debugging a bit to make sure it is still easily usable.

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This is not really needed. I could remove it if you want.

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Update: I just realized some commits are still missing, I'll add them in a moment.

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Remaining stuff is committed.

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@KTrel I hope your deadline stress is (for the moment) over.

Do you have a moment to maybe to a quick dry-run of the new project?

"It works on my machine", but I'd be much more confident to merge if you could confirm that it works!
Basically just making sure that the default settings result in a stable mini-internet where everything works.

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Ping @KTrel

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Yu Chen took the time to confirm that everything is working, as @KTrel currently has their hands full.

Everything worked, so I am merging this now.