Tools: Automate the creation of apm.pdef.xml files

[amilcarlucas]

Whenever a tag is pushed, create the corresponding parameter metadata documentation apm.pdef.xml file on the https://autotest.ardupilot.org/Parameters/versioned/ URL

[peterbarker]

This should be a triggered action on the autotest server, surely?

I'd really rather do this out of build_binaryes.py on the server... which also stares at the tags created and acts on them.