* Adds an achievement for pushing a boulder up a hill (#82813)

## About The Pull Request

Credit to Melbert for this idea.
Adds a new achievement awarded for carrying a boulder from Lavaland to
the Centcom Rescue Wing (via the Escape Shuttle).
If the boulder ever leaves your hands you will not gain the achievement.
If the boulder is not outside on Lavaland when you pick it up you will
not gain the achievement.
If you arrive at the Rescue Ship (via pod) you will not gain the
achievement.
If you drop the boulder 
If the shuttle is hijacked and you do not arrive at Centcom you will not
gain the achievement (perhaps try hitting the hijacker with the boulder
you are not allowed to drop?).
If you arrive at Centcom via the Escape Shuttle but fail to exit the
shuttle holding the boulder (for instance, because a max cap bomb is
detonated next to you one second after the shuttle arrives) you will not
gain the achievement.

As the achievement is rewarded after the round-end report is generated,
you also will not be represented on the round-end report. This is a
personal struggle.

Also carrying a boulder slows you down. Dragging it already did, so I'm
not sure why carrying one did not. It feels like an oversight, and just
makes sense.
People rarely have any particular need to manually carry them anywhere
so this should be fine, right? 🙂

## Why It's Good For The Game

Making players do pointless and weird bullshit is the reason to have an
achievement system.
It's a social experiment.
I think that it is funny.

## Changelog

:cl: Jacquerel and Melbert
add: A new achievement for moving a boulder from one place to another,
at great effort.
balance: Hauling a boulder around makes you move slower, as it does when
dragging it.
/:cl:

* Adds an achievement for pushing a boulder up a hill

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Co-authored-by: Jacquerel <[email protected]>