I'm :+1 for this!
Thanks for the suggestion! it makes 100% sense for the password reminder fields and is in fact a must for these.
For the first one though, I'm not convinced. There seems to be a lot of people arguing against this measure as it breaks the usability of password managers. So I will push the last two autocomplete=off and not first one.
For more info on the pros/cons see: https://startpage.com/do/search?q=autocomplete%3Doff%20security
FYI: because this is actually a great feature request that could be done as a config setting i've reopened an issue for it: New config setting to set autocomplete=off to password fields in Piwik #6347
Feel free to suggest pull request :+1: