Team feature migration tool

[pcapriotti]

Team feature migration tool.

We decided that a data migration is not the best way to move feature configurations to the new table. Instead, this PR adds a new migrate-features tool that can be used to manually perform the migration.

https://wearezeta.atlassian.net/browse/WPB-16238

Checklist

• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[supersven]

We're using this Job manifest to run it on staging:

apiVersion: batch/v1
kind: Job
metadata:
  name: migrate-features
spec:
  template:
    spec:
      containers:
        - name: migrate-features
          image: quay.io/wire/migrate-features:0.0.2-pr.10263
          args:
            [
              --cassandra-host-galley,
              galley-galley-eks-service.databases.svc.cluster.local,
              --cassandra-port-galley,
              "9042",
              --cassandra-keyspace-galley,
              galley,
            ]
      restartPolicy: Never
  backoffLimit: 4

If it succeeds, we may add this ☝️ (with the released image tag) to the docs.