Add topologySpreadConstraints to Flagger helm chart

[frittentheke]

Describe the feature

Allow setting topologySpreadConstraints (https://kubernetes.io/docs/concepts/scheduling-eviction/topology-spread-constraints/) in the flagger Helm chart.

This is just like the spec.deployment.affinity setting allowing to further configure the pod placement.

Proposed solution

Add a parameter topologySpreadConstraints to the values and reference it is the deployment template.

Any alternatives you've considered?