Add ability to customize helm values for deployment strategy

[rmlamarche]

Changes

• Adds ability to customize deployment rollout strategy.type in the wiki helm chart ("RollingUpdate" vs. "Recreate")
• With strategy.type="RollingUpdate", maxSurge and maxUnavailable are also customizable via helm values
• Documentation updated with descriptions/defaults for new helm values

Testing

Default behavior is unchanged (RollingUpdate - 25% - 25%)

$ helm template . | grep -A4 strategy
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%

Rendering with strategy.type set to Recreate

$ helm template --set strategy.type="Recreate" . | grep -A4 strategy
  strategy:
    type: Recreate
  selector:
    matchLabels:
      app.kubernetes.io/name: wiki

Customizing maxSurge

$ helm template --set strategy.rollingUpdate.maxSurge="100%" . | grep -A4 strategy
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 100%
      maxUnavailable: 25%

Customizing maxUnavailable

$ helm template --set strategy.rollingUpdate.maxUnavailable="100%" . | grep -A4 strategy
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 100%