[BUG]: Nextcloud deployment has no liveness probe for php-fpm container

[pmig]

Actual:

Liveness probes are only configured for the nginx container, but not for php-fpm so php hangups are not correctly recognized.

Desired:

Implement liveness probes for php-fpm. We could add a custom shell script to the container and execute it for the liveness e.g.: https://github.com/renatomefi/php-fpm-healthcheck#kubernetes-example

[pmig]

related to #232