add security context for non root user

[bmaguireibm]

This PR would add a security context section to the GeoServer Pod to take into account of the fact that newer docker images of GeoServer runs with a non root user and thus encounters a permissions error when accessing mounted volumes.

[NyakudyaA]

@bmaguireibm Can you check the failing test if it's related to your changes

[bmaguireibm]

Hi @NyakudyaA, I'm afraid I'm not very familiar with these tools very much, but from my investigation it doesn't look related to my changes, the error is Error: direnv: command not found, so it seems like the job is trying to use a binary that's not included in the image that it's running in. Maybe it used to be part of ubuntu-latest and a recent change of the image removed it? I have just tried adding a step beforehand to install direnv, not sure if this is the best approach though.