Feature Request: download room history

[The "Migrate your existing Matrix account" tool](https://ems.element.io/tools/matrix-migration) does quite a good job in transfering your account to a new home server including setting roles and parting the old account, which is quite cool. It does *not* transfer the history though, which is totally plausible from a technical point of view.

Though when migrating to a new home server, leaving years of chat history behind might be a show stopper from finally moving away from matrix.org (which is the case for myself by now). The built-in history download thing from inside Element Web is fine for one or two iterations, but it gets sort of tedious when you have a three-digit number of rooms and dms in your account.

So I was looking for a scriptable solution and found `matrix-commander` having candidate potential. Unfortunately, it does not seem to be able to download a room's history yet, does it? So this is a request for a "download room history" feature.

Look at the existing room interaction commands in matrix-commander to understand the API client setup. The Matrix nio library's sync and room history methods will be needed. Start by reading the project's documentation on adding new commands and examine how other features like message sending are implemented. Test by fetching history for a single room to verify the output format and pagination.

索引モデルが issue の本文から書いたものです。