Including unused substitutions triggers console logs, so change the key backup
panel to only substitute what's actually used in each message.
Fixes https://github.com/vector-im/riot-web/issues/8047.
Adds a New Recovery Method dialog which is shown when key backup fails because
of a version mismatch / version not found error.
The set up button in the dialog currently only marks a device as verified (via a
verification prompt) instead of the eventual restore and cross-sign flow, since
those pieces don't exist yet.
Signed-off-by: J. Ryan Stinnett <jryans@gmail.com>
Continues from Matthew's work: adds a feature flag & panel in
user settings to create a backup.
Can't restore a backup yet, nor even continue backing up to the same
backup after a refresh.
