[Controller] Add adapter hash suffix to Migrations job name

Summary

Adds the CustomResourceAdapter's hash as a suffix to the Migrations Job name (the first 3 characters of the hash).

I couldn't use a random hash because that value would be different every time the controller did a reconcile loop, and would have resulted in a brand new Migrations job deployed upon every loop.

Instead, we use the Adapter hash because that value will change every time the CR values change, which is ultimately what we want anyway.

Note that this is expected to be a temporary workaround. The more complete fix is being discussed in gitlab-org/charts/gitlab#734 (closed).

Closes #216 (closed)

Testing

First, deploy the controller and a CR. Example CR:

apiVersion: apps.gitlab.com/v1beta1
kind: GitLab
metadata:
  name: gitlab
spec:
  chart:
    version: "5.1.1"
    values:
      certmanager:
        install: false
      global:
        hosts:
          domain: yourdomain.com
          configureCertmanager: false

Wait for all pods to be up and running.

Next, update the CR with a new value. Example:

apiVersion: apps.gitlab.com/v1beta1
kind: GitLab
metadata:
  name: gitlab
spec:
  chart:
    version: "5.1.1"
    values:
      certmanager:
        install: false
      global:
        hosts:
          domain: yourdomain.com
          hostSuffix: foo # added this configuration
          configureCertmanager: false

Apply the CR and observe that a second Migrations job is created, with a different suffix. (In the past, this second job would not have been created because it would have had the same name as the previous one.)

$ kubectl get jobs -n gitlab-system -lapp=migrations
NAME                      COMPLETIONS   DURATION   AGE
gitlab-migrations-1-836   1/1           67s        11m
gitlab-migrations-1-a75   1/1           84s        8m7s