Disable the default site of apache and nginx on demand

Adds support for Debian 10 Buster

Pointed out by @aalaesar during review. In short, libmcrypt has been
obsolete since PHP 7.1 and removed since PHP 7.2. Therefore, we'll
preserve the installation of the package on older platforms
(specifically 5 & 7.0), but skip it on newer platforms (such as 7.2,
7.3). See for details [0].

[0] https://lukasmestan.com/install-mcrypt-extension-in-php7-2/

Mostly it's the PHP version bump, 7.0 -> 7.3. One of the PHP packages
doesn't exist in the Buster repos, so added conditional logic to
preserve it by default, but omit specifically when PHP == 7.3.

Added support for Multi os

Security issue in NGINX/php-fpm

Update nginx conf due to this security issue : https://nextcloud.com/blog/urgent-security-issue-in-nginx-php-fpm/

I'm not an expert of php-fpm so I've just applied the recommended corrections. I did the update on my own configuration and it works.
If something goes wrong on my side I'll inform you.

 Fixing 'Your web server is not properly set up to resolve "/ocm-provider/".'

Fix error:
>You are reading an outdated version of this documentation. Please check out the latest version of the server administration manual.

Fixing 'Your web server is not properly set up to resolve "/ocm-provi…

Fixing this error:
```
There are some warnings regarding your setup.
    Your web server is not properly set up to resolve "/ocm-provider/". This is most likely related to a web server configuration that was not updated to deliver this folder directly. Please compare your configuration against the shipped rewrite rules in ".htaccess" for Apache or the provided one in the documentation for Nginx at it's documentation page. On Nginx those are typically the lines starting with "location ~" that need an update.
```

Using code from here:
https://docs.nextcloud.com/server/16/admin_manual/installation/nginx.html

typo in readme

Feature: add maximum upload size parameter

by calculating max upload size in byte outside of the templates

 Using ipwrap on templates to add brackets when it is needed