Schema Validation for Strategy

Related to #1 (closed).

Make a values.json.schema that enforces the strategy values that are supported. See https://www.arthurkoziel.com/validate-helm-chart-values-with-json-schemas/ for more info:

{
  "$schema": "http://json-schema.org/schema#",
  "type": "object",
  "required": [
    "strategy"
  ],
  "properties": {
    "imagePullPolicy": {
      "type": "string",
       "pattern": "^(monolith|scalable|microservice)$"
    }
  }
}