Move LICENSE file for kubectl-plugin from public/ to cmd/ (#282)

# Summary

As part of [the
PR](#271) we moved the
kubectl-mongodb code from `public/tools/multicluster` to
`cmd/kubectl-mongodb`.
This PR, tries to move the license file from `public/tools/multicluster`
to `cmd/kubectl-mongodb`.
The next [PR](#281) in
this chain are going to actually remove the `public/tools` directory
entirely.

## Proof of Work

NA

## Checklist
- [x] Have you linked a jira ticket and/or is the ticket in the title?
- [x] Have you checked whether your jira ticket required DOCSP changes?
- [x] Have you checked for release_note changes?

Author: viveksinghggits