Document import/export Dashboard API

[tylersmalley]

Originally introduced in #10858, we should add documentation for this tagged experimental.

Export:
curl -XGET localhost:5601/api/kibana/dashboards/export?dashboard=[dashboard_uuid] > my-dashboards.json

Import:
curl -XPOST localhost:5601/api/kibana/dashboards/import -H 'kbn-xsrf:true' -H 'Content-type:application/json' -d @my-dashboards.json

[mnp]

I am interested in exporting everything from one system and importing it into another. The use case would be developing searches, visualizations, and dashboards on a dev instance by hand, saving it off as a work product, and then automatically importing it into new instances at install time. So far I've gotten this working by hand with the small extra step of identifying the UUID of the default index in the exported JSON and replacing (sed) it with the UUID of the default index in the destination system.

[ossindayigaya]

I'm working on using the above import and export dashboard endpoints in production (running 5.6.4). Is there anything I'm missing to leverage these endpoints? I'm currently getting an illegal_argument_exception due to request [/kibana/dashboards/export] contains unrecognized parameter: [dashboard] and I'm using api/kibana/dashboards/export?dashboard=AWUQ9qG5OA9KEA5JT1Ug