Allow to customize the livenessProbe for `gitlab-shell`

I've mostly followed how a similar change was done in !985 (merged).

Related to #1576.

Tested with

› helm template . --set certmanager-issuer.email=foo@bar.com --set gitlab.gitlab-shell.deployment.livenessProbe.initialDelaySeconds=42 --set gitlab.gitlab-shell.deployment.livenessProbe.periodSeconds=66 --set gitlab.gitlab-shell.deployment.livenessProbe.timeoutSeconds=99 --set gitlab.gitlab-shell.deployment.livenessProbe.successThreshold=12 --set gitlab.gitlab-shell.deployment.livenessProbe.failureThreshold=13 -x charts/gitlab/charts/gitlab-shell/templates/deployment.yaml

---
# Source: gitlab/charts/gitlab/charts/gitlab-shell/templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: release-name-gitlab-shell
  namespace: review-apps-ee
  labels:
    app: gitlab-shell
    chart: gitlab-shell-2.4.5
    release: release-name
    heritage: Tiller
    
spec:
  selector:
    matchLabels:
      app: gitlab-shell
      release: release-name
  template:
    metadata:
      labels:
        app: gitlab-shell
        release: release-name
      annotations:
        checksum/config: caa9515adf5c7a14e7792c46cb18a221c9aea5e3267222a81bdaf0b31c3f8020
        cluster-autoscaler.kubernetes.io/safe-to-evict: "true"
    spec:
      initContainers:
        
        
        - name: certificates
          image: "registry.gitlab.com/gitlab-org/build/cng/alpine-certificates:20171114-r3"
          
          volumeMounts:
          - name: etc-ssl-certs
            mountPath: /etc/ssl/certs
            readOnly: false
          resources:
            requests:
              cpu: 50m
            
        - name: configure
          command: ['sh', '/config/configure']
          image: busybox:latest
          volumeMounts:
          
          - name: shell-config
            mountPath: /config
            readOnly: true
          - name: shell-init-secrets
            mountPath: /init-config
            readOnly: true
          - name: shell-secrets
            mountPath: /init-secrets
            readOnly: false
          resources:
            requests:
              cpu: 50m
            
      securityContext:
        runAsUser: 1000
        fsGroup: 1000      
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 1
            podAffinityTerm:
              topologyKey: kubernetes.io/hostname
              labelSelector:
                matchLabels:
                  app: gitlab-shell
                  release: release-name
      containers:
        
        - name: gitlab-shell
          image: "registry.gitlab.com/gitlab-org/build/cng/gitlab-shell:latest"
          
          ports:
            - containerPort: 2222
              name: ssh
          env:
            - name: GITALY_FEATURE_DEFAULT_ON
              value: "1"
            - name: CONFIG_TEMPLATE_DIRECTORY
              value: '/etc/gitlab-shell'
            - name: CONFIG_DIRECTORY
              value: '/srv/gitlab-shell'
            - name: KEYS_DIRECTORY
              value: '/etc/gitlab-secrets/ssh'
          volumeMounts:
            - name: shell-config
              mountPath: '/etc/gitlab-shell'
            - name: shell-secrets
              mountPath: '/etc/gitlab-secrets'
              readOnly: true
            
            - name: etc-ssl-certs
              mountPath: /etc/ssl/certs/
              readOnly: true
          livenessProbe:
            exec:
              command:
              - /scripts/healthcheck
            initialDelaySeconds: 42
            periodSeconds: 66
            timeoutSeconds: 99
            successThreshold: 12
            failureThreshold: 13
          # readinessProbe:
          #   httpGet:
          #     path: /
          #     port: 2222
          resources:
            requests:
              cpu: 0
              memory: 6M
            
      volumes:
      
      - name: shell-config
        configMap:
          name: release-name-gitlab-shell
      - name: shell-init-secrets
        projected:
          defaultMode: 0440
          sources:
            - secret:
                name: "release-name-gitlab-shell-host-keys"
            - secret:
                name: "release-name-gitlab-shell-secret"
                items:
                  - key: "secret"
                    path: shell/.gitlab_shell_secret
            - secret:
                name: "release-name-redis-secret"
                items:
                  - key: "secret"
                    path: redis/password
      # Actual config dirs that will be used in the container
      - name: shell-secrets
        emptyDir:
          medium: "Memory"
      
      - name: etc-ssl-certs
        emptyDir:
          medium: "Memory"

Closes #1669 (closed).