Add docs for our cronjobs

docs/recurring-tasks.md

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+### Recurring tasks on the Green Web Platform
+
+The Green Web Foundation platform relies on a number of regular tasks run by scripts, that happen on a daily, or weekly basis.
+
+To make it easier to maintain and track configuration drift (i.e. small changes in leading to unexpected behaviour), these are kept in source control as role and playbooks in Ansible.
+
+
+```{admonition} Draft
+A number of these cronjobs were set up manually before by green web foundation staff. As these jobs are moved under configuration management in source code they will be added to the documentation here.
+```
+
+### Weekly imports
+
+While the Green Web Foundation offers a self-service way to maintain up to date lists of IP ranges and AS numbers, historically we maintained a set of automated importers of IP ranges for a small number of large providers of hosted services. These providers who publish their IP ranges in a machine-readable format at public endpoints our systems can access, then import into the corresponding provider's lists of AS numbers and IP ranges. 
+
+These can be run on the command line using the following commands
+
+```
+./manage.py update_networks_in_db_amazon
+./manage.py update_networks_in_db_google
+./manage.py update_networks_in_db_microsoft
+```
+
+Look in the `import_ips_for_large_providers.sh.j2` file to see the specific shell script run each week, and the `setup_cronjobs.yml` ansible playbook to see the specific tasks used to set up a a server to run these on a recurring schedule.
+
+#### Defining the cronjob
+
+Using 
+
+```yaml
+- name: Ensure job to run IP hyperscaler importers is present
+  ansible.builtin.cron:
+    name: "every Wednesday at 2:30 run our importers"
+    state: present
+    weekday: "WED"
+    hour: "2"
+    minute: "30"
+    user: deploy
+    job: >
+      bash /home/deploy/cronjobs/import_ips_for_large_providers.sh 
+      >> /var/log/import_ips_for_large_providers.log 
+      2>> /var/log/import_ips_for_large_providers.error.log
+  tags: [crontab]
+```
+
+Here in this snippet of ansible code, we run a script, each week, and we pipe the output into a dedicated log file (see `>> /var/log/import_ips_for_large_providers.log`), along with piping any errors into a dedicated error log file (see the `2>>` part to pipe STDERR into `/var/log/import_ips_for_large_providers.error.log`).
+
+We use the yaml folded scalar literal to make the formatting easier to read, along with the time we want the job to run.
+
+#### Checking that the cronjobs are on the server
+
+If you wanted to check that a cronjob is set up on the necessary server, you would run the following ansible command, passing in the correct inventory file to tell ansible which set of servers to connect to, and passing in `--check`` to see what changes might take effect:
+
+```
+pipenv run ansible-playbook -i ansible/inventories/prod.yml ansible/setup_cronjobs.yml --check
+```
+
+To run the actual command, and update the cronjobs, you would run the same command, without the `--check` flag.
+
+```
+pipenv run ansible-playbook -i ansible/inventories/prod.yml ansible/setup_cronjobs.yml
+```
+
+### Daily Green Domain Exports
+
+TODO: add docs here for this cronjob too.