UI should use subchart defaults, if any, when installing/upgrading a chart

[slickwarren]

on master-head e756276: Repro Steps:

• deploy rancher
• deploy downstream cluster large enough for longhorn and monitoring
• install longhorn
• install monitoring
  • use a statefulset for grafana when installing monitoring
  • do not enter any values for the statefulset

I expected this to break the monitoring install, but instead: monitoring will install and use default values from grafana, using longhorn as the PV. After further investigation, it appears there are defaults in the subchart, Grafana. However, even after the successful install, the values.yaml don't reflect the values used from the subchart (from the repro steps, values.yaml -> grafana -> size still read as null , even though the is working as expected and is using a 10Gi PV in longhorn)

We should populate subchart defaults in the UI when applicable. This is likely the case for other charts as well, as many of our v2 charts use subcharts on install.