fix(chart): remove unused volume mounts and DB secret from nginx container

[danielqb]

Problem

The nginx container in glpi-deployment.yaml mounted the files, marketplace,
and etc PersistentVolumeClaims (ReadWriteOnce) even though nginx's actual
config (default.conf) never reads from those paths - it only serves static
assets from /var/www/html/public (baked into the image) and proxies
everything else to php-fpm via fastcgi_pass. It also pulled glpi-secret
(DB credentials) via envFrom despite never connecting to the database.

Since both nginx and php-fpm mounted the same RWO PVCs, a cluster without
explicit pod affinity forcing them onto the same node could schedule them
on different nodes, causing FailedMount/ContainerCreating for whichever
pod lands second.

Fix

Removed the files/marketplace/etc volumeMounts and volumes, and the
glpi-secret envFrom, from the nginx container. Only php-fpm (which is
the only container that actually touches GLPI_VAR_DIR/marketplace/etc
and the database) keeps these. nginx now only mounts nginx-conf.

This also reduces blast radius: nginx no longer has DB credentials in
its environment (least privilege).

Testing

• helm lint: 0 failures
• helm template: nginx Deployment renders with only nginx-conf volume,
  no envFrom block

[eduardofraga]

This project requires RWX persistent volume claim because php-fpm and nginx access same volume.