Merge spec.container with the default one not overwrite it

## Expected Behavior
I need to modify some aspects of the `spec.container` section, for example, I need to add initialDelaySeconds in startupProbe (I use Istio and the proxy container restarts before its first successful launch due to Istio). However, I can't do this without rewriting the entire container section, which I believe isn't not only complex, but also not appropriate.

## Actual Behavior
I am forced to overwrite the entire container section.

## Steps to Reproduce the Problem
n/a

## Specifications

- Version: v1.4.1
- Platform: GKE