Command line flag for clearing cache and reloading

[Mikaela]

Description

I am on family desktop which I at times don't use for months and Riot seemed to freeze at times and be showing old messages. I wish I could clear cache and reload without opening Riot and I think a command line flag would be a good place for it.

I also hit element-hq/element-web#3734 as flatpak run im.riot.Riot --help just launches the app as usual, but I managed to clear cache and reload and am hoping it will fix the issue prompting me to open this.

Version information

• Platform: desktop

For the desktop app:

• OS: Debian GNU/Linux buster/sid
• Version: 1.0.1 (the template is still 0.x.y by the way) (PR for 1.0.3 Update Riot to version 1.0.3 flathub/im.riot.Riot#36)