Added topologySpreadConstraints value

What does this MR do?

This MR adds topologySpreadConstraints value for deployment template.

Why was this MR needed?

Adds topologySpreadConstraints to control how GitLab runner Pods are spread across the cluster To resolve issue #359 (closed)

What's the best way to test this MR?

1. Create values-test.yaml file with following content

---
topologySpreadConstraints:
  - maxSkew: 1 
    topologyKey: topology.kubernetes.io/zone 
    whenUnsatisfiable: DoNotSchedule 
    labelSelector: 
      matchLabels:
        foo: bar

2. Run helm template ./ -f values-test.yaml
3. Rendered deployment template should contain topologySpreadConstraints section

.....
- name: configmaps
  configMap:
    name: release-name-gitlab-runner
topologySpreadConstraints:
  - labelSelector:
      matchLabels:
        foo: bar
    maxSkew: 1
    topologyKey: topology.kubernetes.io/zone
    whenUnsatisfiable: DoNotSchedule
...

What are the relevant issue numbers?

Closes #359 (closed)