Remove requirements.yaml, due to Helm 3 changes

Helm 3 merges requirements.yaml into Chart.yaml.
I tested this config with the CI and it works fine, it seems only fitting to remove requirements.yaml from the documentation. as it's depricated, every new chart uploaded to the repo should have it copy-pasted into the Chart.yaml (the syntax is still the same)

Add plex/minio/nextcloud/ix-chart to stable train

Take backup of postgres on helm upgrade

Use nc instead of nslookup while waiting for postgres to come up

Make sure hostports are not used when update strategy is rolling update

Using nslookup, the wait time for nextcloud pod to come up can be up to 1-5 minutes. This is reduced with nc to 5-10 seconds.

Update version for minio/nextcloud/plex charts

Add Minio Chart