Create trafikverket_ferry integration (#22476)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

source/_integrations/trafikverket_ferry.markdown

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+---
+title: Trafikverket Ferry
+description: Instructions how to integrate Trafikverket Ferry within Home Assistant.
+ha_category:
+  - Sensor
+  - Transport
+ha_release: 2022.5
+ha_iot_class: Cloud Polling
+ha_config_flow: true
+ha_codeowners:
+  - '@gjohansson-ST'
+ha_domain: trafikverket_ferry
+ha_platforms:
+  - sensor
+ha_integration_type: integration
+---
+
+Retrieve ferry departure information from [Trafikverket](https://www.trafikverket.se/).
+
+## Prerequisites
+
+Please click [here](https://api.trafikinfo.trafikverket.se/) and register to obtain the API key.
+
+{% include integrations/config_flow.md %}
+
+## Use cases
+
+- Retrieve the next departure and information connected to it.
+- Destination harbor is optional and by leaving it empty it will show the next destination available from the selected departure harbor.
+- By choosing a specific time it will only show departures after this.
+- By deselecting from the pre-filled days of the week you can make selections such as only Monday to Friday if needed.
+
+## Sensors
+
+- Next departure date and time by made selections.
+- Departure harbor.
+- Destination harbor.
+- Modified time (this sensor is deactivated as standard).
+
+Other information provided by Trafikverket related to the specific departure is shown as attribute on all sensors.
+
+## Ferry harbour names
+
+Click [here](https://www.trafikverket.se/trafikinformation/vag/?TrafficType=personalTraffic&map=1/373767.82/6890962.41/&Layers=Ferries%2b) to see examples of harbor names, use city name as harbor, as for example "Ekerö", "Svanesund".