Add amd64 architecture node selector to velero and velero-plugin-for-aws

[pregnor]

Is your feature request related to a problem? Please describe.

In order to be able to use mixed architecture clusters while only single architecture velero-pluging-for-aws images are available, we want to add a node selector to both velero and velero-plugin-for-aws containers which forces the containers onto amd64 nodes.

Describe the solution you'd like to see

Add a kubernetes.io/arch node selector set to amd64 value to the velero and velero-plugin-for-aws components' chart values to force the these containers to be scheduled on amd64 nodes until the multi-architecture ARM support is available for both containers.

Describe alternatives you've considered

Architecture based tainting using an operator.

Additional context

One solution is to extend the Velero configuration at internal/ark/config.go.ValueOverrides and the inlined init container configurations (based on provider) with the necessary node selector (the chart already supports it through the top level nodeSelector key).