Mixed worker configuration is not possible

# Issue
Running workers with different configuration is not possible, e.g. one with `nvidia.com/gpu` and one with `amd.com/gpu`

```yaml
Worker:
replicas: 1
template:
spec:
containers:
- image: mpioperator/tensorflow-benchmarks:latest
name: tensorflow-benchmarks
resources:
limits:
nvidia.com/gpu: 2
```

# Why is this relevant
Being able to use different GPU models or vendors is a feature users ask for.

# Solution
Maybe supporting a configuration for specific workers would solve it.

```yaml
Worker-1:
template:
spec:
containers:
- image: mpioperator/tensorflow-benchmarks:latest
name: tensorflow-benchmarks
resources:
limits:
nvidia.com/gpu: 2
Worker-2:
template:
spec:
containers:
- image: mpioperator/tensorflow-benchmarks:latest
name: tensorflow-benchmarks
resources:
limits:
amd.com/gpu: 2
```

I am happy to contribute if this feature is wanted.