Add ability to export programatically via web service keys

[brendanheywood]

See:

https://github.com/moodleou/moodle-report_customsql/pull/106/changes

[marcusgreen]

Good idea. I will put it on the list

[brendanheywood]

As long as you offer download via pluginfile api and are using the dataformat api then you get the webservice side for free. I think we need to offer this directly against the source and in parallel we'll also land this adds it to report builder itself:

https://moodle.atlassian.net/browse/MDL-73291