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Apache website config files are located in /etc/apache2/sites-available/ directory.
In this case I'm using fictional example.com website domain name.
Browse to that dir, then you could copy 000-default.conf file to example.com.conf or simply create brand new one and then copy-paste the following config/code block there:
<VirtualHost *:80>
DocumentRoot "/var/www/example.com"
ServerName example.com
ServerAlias www.example.com
<Directory "/var/www/example.com">
allow from all
Require all granted
</Directory>
RewriteEngine on
RewriteCond %{SERVER_NAME} =example.com [OR]
RewriteCond %{SERVER_NAME} =www.example.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>
When you create Letsencrypt SSL https domain config for your website domain, it will most likely complain about that RewriteCond/RewriteRule that its disabled because it might lead into never ending loop. I have no idea about that, I need to figure it out later :) PMCTODO