Add NodeSelector support to linkerd-failover chart

[bezarsnba]

• This PR adds support for nodeSelector to the linkerd-failover chart. This allows users to specify which nodes in their Kubernetes cluster should be used to run the linkerd-failover pods.

This is useful for scenarios where you want to:

• Run linkerd-failover on specific nodes with certain resources or hardware. For example, you might want to run it on nodes with more memory or specific hardware capabilities.
• Isolate linkerd-failover pods from other workloads. This can be useful for security or performance reasons.

The nodeSelector option can be set in the values.yaml file of the chart.

Using

Users can utilize NodeSelector by setting the corresponding fields in the linkerd-failover graph values ​​file:

nodeSelector: 
  kubernetes.io/os: linux

Tests:

This PR includes unit and integration tests to ensure that NodeSelector works correctly. The tests were carried out in GKE.

Output of kubectl apply:

k get pods linkerd-failover-7fbbf98cf9-2pr4l -o jsonpath='{.spec.nodeSelector}'
{"kubernetes.io/os":"linux"}