feat: Define cron jobs running mgmt commands in Helm chart

[microamp]

Fixes #431.

• Two cron jobs:

  The PR defines two cron jobs, one hourly the other weekly.

  https://docs.wagtail.org/en/stable/reference/management_commands.html

  • publish_scheduled:

    We recommend running this command once an hour.

  • update_index:

    It is recommended to run this command once a week

  With the current spec, the daily job runs every hour at minute 0, and the weekly job runs on Sunday at 00:30 UTC. Note that the weekly database maintenance window currently occurs on Saturdays UTC, and will no overlap with the weekly cron job.

• Verifying helm install output:

  With tag set to the latest image tag, v2.1.10, helm install www helm --dry-run outputs as below.

  ...
  ---
  # Source: www/templates/cronjob.yaml
  apiVersion: batch/v1
  kind: CronJob
  metadata:
    name: "mgmt-hourly"
  spec:
    schedule: "0 * * * *"
    timeZone: "Etc/UTC"
    concurrencyPolicy: Forbid
    jobTemplate:
      spec:
        backoffLimit: 0 # No retries
        template:
          spec:
            restartPolicy: Never
            volumes:
              - name: settings-local-volume
                configMap:
                  name: django-configmap
            containers:
            - name: "mgmt-hourly"
              image: "ghcr.io/ietf-tools/www:v2.1.10"
              imagePullPolicy: IfNotPresent
              ...
              command: ["python","/app/manage.py","publish_scheduled"]
  ---
  # Source: www/templates/cronjob.yaml
  apiVersion: batch/v1
  kind: CronJob
  metadata:
    name: "mgmt-weekly"
  spec:
    schedule: "30 0 * * 0"
    timeZone: "Etc/UTC"
    concurrencyPolicy: Forbid
    jobTemplate:
      spec:
        backoffLimit: 0 # No retries
        template:
          spec:
            restartPolicy: Never
            volumes:
              - name: settings-local-volume
                configMap:
                  name: django-configmap
            containers:
            - name: "mgmt-weekly"
              image: "ghcr.io/ietf-tools/www:v2.1.10"
              imagePullPolicy: IfNotPresent
              ...
              command: ["python","/app/manage.py","update_index"]

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.81%. Comparing base (271b518) to head (adff04c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #440 +/- ## ======================================= Coverage 82.81% 82.81% ======================================= Files 126 126 Lines 2612 2612 ======================================= Hits 2163 2163 Misses 449 449 ```

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