Default to not making history available in encrypted rooms

[madduck]

Members joining an encrypted room won't have the keys to messages in the history (while element-hq/element-web#6545 is unresolved). Thus, the first thing they might see upon joining a new room is a slew of messages about messages that can't be decrypted.

In element-hq/element-web#6837, it was suggested to disable the setting to make history available in encrypted rooms. This might go too far.

How about defaulting to not making history available in encrypted rooms though? That would probably already lessen potential confusion?

[JorikSchellekens]

I just migrated home servers. A power user would like to view messages in a room for which they have the keys for on another device because they know the keys can be imported. Could we make it so that the history is not shown by default, instead displaying a message stating that history exists with the explicit caveat that you probably can't decrypt them and finally allow the visibility to be configure per room?

This could be enormously beneficial to modular users