Add DepotDownloader as alternative to steamcmd

[sonroyaalmerol]

Context

There has been a lot of cases where ARM64 users are having trouble with steamcmd in general. The main idea for this PR is to give an alternate way for the container to download game server files without using steamcmd. This should hopefully bring back compatibility with M-series Macs (closes #556).

This will also completely remove the 4k page size limitations we had previously as that was mostly due to steamcmd. (#456, #397)

This should also allow us to go back to using Github hosted runners for the unit tests as long as USE_DEPOT_DOWNLOADER is set to true when executed for ARM64.

Might also help other unrelated steamcmd problems (e.g. #551)

DepotDownloader: https://github.com/SteamRE/DepotDownloader

Choices

We can force ourselves to emulate steamcmd, which has been proven to be very finicky due to the fact that Valve don't ship steamcmd as a 64-bit binary. Or we can go and use open-source tools to download the server files like DepotDownloader.

Test instructions

1. Set USE_DEPOT_DOWNLOADER to true
2. Run the container as usual

Checklist before requesting a review

• I have performed a self-review/test of my code
• I've added documentation about this change to the docs.
• I've not introduced breaking changes.
• My changes do not violate linting rules.

[sonroyaalmerol]

@thijsvanloef i'd also appreciate if you could publish a test image tag for this as well so they could easily test 🙏

[thijsvanloef]

Here is the image:
thijsvanloef/palworld-server-docker:arm-test

[sonroyaalmerol]

This should be good to go :) I'll be working on the other pr as soon as this is merged.