chore: Make workers replicas configurable

[imusmanmalik]

Replicas for worker machines are not configurable, hence when generating using:

clusterctl generate cluster t-cluster --infrastructure=maas:v0.5.0 --kubernetes-version v1.26.4 --control-plane-machine-count=1 --worker-machine-count=2  > maas-cluster-api.yaml

--worker-machine-count=2 is not reflected in the generated MachineDeployment spec.replicas as its hardcoded and not templated.

Tested by providing overrides:

├── overrides
│   └── infrastructure-maas
│       └── v0.5.0
│           └── cluster-template.yaml

[imusmanmalik]

@sadysnaat is there anything else that is blocking to merge this in ?