Add s&box engine

[nixxquality]

SteamDB app page links to a few games using this

https://steamdb.info/app/590830/ (s&box itself)
https://steamdb.info/app/3115420/ (My Summer Cottage)

Brief explanation of the change

Here are some pages that explain the standalone publishing in s&box:

• https://sbox.game/news/august-update-4b1b55d9#standalone-exporting
• https://sbox.game/news/january-update-6a7d5bb1#standalone
• https://sbox.game/dev/doc/

As of writing, Valve is still "checking over" their publishing agreement, and officially standalone publishing is not yet allowed. This is what the editor says:

As I understand it, My Summer Cottage has a special deal with Facepunch which allows them to publish regardless.

I understand if you want to hold off on merging this until a few more games join the ranks.

[Lifeismana]

imo, not worth merging until s&box releases

[SteamDB-Tracker]

After running changed rules in this pull request (this bot only tests rules.ini changes):

Changed technologies: Engine.sandbox

These apps now match: (4) 590830 1892930 2722020 3115420

Please confirm that all these changed apps are correct.

[nixxquality]

Just keeping information up to date; s&box released on Steam back in late April.
According to the s&box documentation, exporting standalone games is currently allowed only on a per-case basis with permission from Valve.

There are at least two more upcoming games on Steam that use the engine; Hobnobbers and Puddle Pond.
There's also this game which seemingly launched without permission.

I don't know what the qualifier is for an amount of apps that warrants inclusion, but I believe it might be time for another scan at least.