As deleteoldfiles php.ini for each project on Ubuntu?

I agree with the previous answer about Docker. But if you want all the same configs to do that in Apache it's done quite simply. With nginx too, just go you will not write how. In General, for Apache:
Under each project is a separate VirtualHost with a separate configuration file in the directory /etc/apache2/sites-available. And for each VirtualHost'a register change the default PHP config. These changes will apply only to requests to this VirtualHost'.
That is what I had written for Bitrix:

php_admin_flag short_open_tag On php_admin_value opcache.revalidate_freq to 0 php_admin_value mbstring.func_overload 2 php_admin_value mbstring.internal_encoding UTF-8 php_admin_value max_input_vars 10000 php_admin_value upload_max_filesize 5M

To change the version of PHP is enough to disable the Apache module with the same version, and on the other to connect:
sudo a2dismod php7.2 && sudo a2enmod php7.0

Docker for prod.
Locally can be Docker or vagrant

PS. I would prefer Docker