Clarify service requirements in manifest.json

[tituspijean]

Right now, the services requirements checks are a bit convoluted and boil down to checking that the following services are OK:

• nginx is always added whatever the provided list
• php7.3-fpm, replacing any other mention of php in the manifest
• mysql
• postfix
• fail2ban is always added whatever the provided list

Other services are ignored, in opposition to the documentation:

services: services needed by the application among nginx, php5-fpm, mysql, uwsgi, metronome, postfix, dovecot…

I suggest we either:

• simplify the checks, acknowledge the limits of the services list in the documentation, and add linter warnings about custom services
• expand the checks, and specify in the documentation that these checks only test for the services being OK and will not try to install them.

[alexAubin]

Eh I was about to say "this is sort of fixed by the manifestv2" but in fact I might have dropped entirely the key and now no checks happens for v2 app ? Need to check the code ...