In order to be able to force the http to https redirection when using wordpress in dreamhost use the following (taken from https://help.dreamhost.com/hc/en-us/articles/215747758-Force-your-site-to-load-securely-with-an-htaccess-file) :
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301,NE]
Header always set Content-Security-Policy "upgrade-insecure-requests;"
# BEGIN WordPress
.....
# END WordPress