feat(matchmake-extension): Support additionalParticipants in AutoMatchmakeWithParamPostpone

[ashquarky]

Resolves https://github.com/PretendoNetwork/splatoon/issues/3

Changes:

Implements moving players between sessions via additionalParticipants. Moving involves skipping disconnecting and migrating hosts, and just moves the connection from one room to another (with an accompanying SwitchGathering call). This happens for all participants and the caller.

Code is pretty thoroughly commented so I won't wax on it too much here.

• [x] I have read and agreed to the Code of Conduct.
• [x] I have read and complied with the contributing guidelines.
• [x] What I'm implementing was an approved issue. (Approved on Splatoon repo)
• [x] I have tested all of my changes.

[ashquarky]

Focusing on #35 for the time being