docs: Add initial documentation

docs/admin/monitoring.rst

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+Monitoring
+==========
+
+ILMO should, like every other software, be easy to monitor. Therefore a basic metrics are exposed to `https://notfellchen.org/metrics`.
+The data is encoded in JSON format and is therefore suitable to bea read by humans and it is easy to use it as data source for further processing.
+
+
+Exposed Metrics
+---------------
+
+.. code::
+
+   users: number of users (all roles combined)
+   staff: number of users with staff status
+   adoption_notices: number of adoption notices
+   adoption_notices_by_status: number of adoption notices by major status
+   adoption_notices_without_location: number of location notices that are not geocoded
+
+Example workflow
+----------------
+
+To use the exposed metrics you will usually need a time series database and a visualization tool.
+
+As time series database we will utilize InfluxDB, the visualization tool will be Grafana.
+
+InfluxDB and Telegraf
+^^^^^^^^^^^^^^^^^^^^^
+
+First we install InfluxDB (e.g. with docker, be aware of the security risks!).
+
+.. code::
+
+   # Pull the image
+   $ sudo docker pull influxdb
+
+   # Start influxdb
+   $ sudo docker run -d -p 8086:8086 -v influxdb:/var/lib/influxdb --name influxdb influxdb
+
+   # Start influxdb console
+   $ docker exec -it influxdb influx
+   Connected to http://localhost:8086 version 1.8.3
+   InfluxDB shell version: 1.8.3
+   > create database monitoring
+   > create user "telegraf" with password 'mypassword'
+   > grant all on monitoring to telegraf
+
+.. note::
+   When creating the user telegraf check the double and single quotes for username an password.
+
+Now install telegraf and configure `etc/telegraf/telegraf.conf`. Modify the domain and your password for the InfluxDB database. 
+
+.. literalinclude:: example.telegraf.conf
+    :linenos:
+    :language: python
+
+Graphana
+^^^^^^^^
+
+Now we can simply use the InfluxDB as data source in Grafana and configure until you have
+beautiful plots!
+
+.. image:: monitoring_grafana.png