Add support for Toolbox's restore PersistentVolumeClaim

What does this MR do?

Add support for restore toolbox persistent volume claim

The toolbox supports two PVCs:

• one for backups, mounted to the backup CronJob's Pod
• another one for restores, mounted to the general toolbox Pod

The latter has not been created/reconciled by the Operator.

Closes #1483 (closed)

Changelog: fixed

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Test Plan

1. Create/update a GitLab CRD to enable both PVCs
2. Confirm both PVCs are created
3. Confirm the Toolbox Pod (created for the Deployment) stats and mounts the gitlab-toolbox-tmp PVC

apiVersion: apps.gitlab.com/v1beta1
kind: GitLab
metadata:
  name: gitlab
  namespace: gitlab-system
spec:
  chart:
    values:
      gitlab:
        toolbox:
          backups:
            cron:
              enabled: true
              persistence:
                enabled: true
                size: 1G
          persistence:
            enabled: true
            size: 1G
    version: 7.8.0

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.