fix: allow certs to be loaded on readonly filesystems

[rarmatei]

if someone uses:

  readOnlyRootFilesystem: true

we can't load any custom certs.

This PR:

1. loads in a volume where the Java certs are located. This bypasses the above readonly setting for that folder only.
2. create an init container based on the same nxcloud image that copies the default certs in that folder to an empty volume
3. when the main container starts and the volume is loaded in, the default are correctly restored
4. now that the folder is writeable, we can continue with the process of loading in the certs