Support modifying pod templates of the pods that tempo operator creates

[markustoivonen]

Currently its not possible to modify the pod templates of the pods created by the tempo operator.

In our use case this means that we cannot apply relevant security policies that must exist in pods inside our cluster.

This type of feature is supported by many other CRDs, e.g. Apache Flink Operator

[siegenthalerroger]

This would also enable setting the securityContext as required in #996