[WIP] Vitess Operator example

[enisoc]

This is still a work in progress, but cluster startup works.

Next steps:

• Rebase on the new Vitess templates in Update helm install for Kubernetes and add new k8s Docker image vitessio/vitess#3487.
• Add back Orchestrator integration as in the old Vitess Helm chart.
• Implement Vitess-specific rolling update strategy for tablets: keyspace-by-keyspace, shard-by-shard, reparent before updating master.
• Automatically initialize replication on new shards.

cc @derekperkins

Vitess Operator

This is an example of an app-specific Operator, in this case for Vitess, built with Metacontroller.

It's meant to demonstrate the following patterns:

• Building an Operator for a complex, stateful application out of a set of small Lambda Controllers that each do one thing well.
• Replacing static, client-side template rendering with Lambda Controllers, which can adjust based on dynamic cluster state.
• Using a functional-style language (Jsonnet) to define Lambda Controllers in terms of template-like transformations on JSON objects.
• Using the "Apply" update strategy feature of CompositeController, which emulates the behavior of kubectl apply, except that it attempts to do pseudo-strategic merges for CRDs.

See the README for more details.

[derekperkins]

This looks great! Time to learn jsonnet :)