[Feature] Fleet: Allow user to drain a cluster for all the resources placed by fleet

**Is your feature request related to a problem? Please describe.**
User wants to drain all the workloads from a cluster before upgrading it.

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**Describe the solution you'd like**
A simple command similar to `kubectl drain node` to drain a cluster

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.