Add to Kicad 6 plugin & content manager

[DavidJRobertson]

It would be nice if this plugin could be added to the PCM for easy installation. See https://www.kicad.org/blog/2021/12/Development-Highlight-Third-Party-Content-Improvements/

[NilujePerchut]

It is definitely on the roadmap.
This is the next step after merging the V6 branch into master (which is taking some times due to #40)

[WhiteChairFromIkea]

Just a note, that v6.99 already has (half a year already) native teardrops (with more advanced features, like adding necks when thinner track intersects thicker one). There is no need for this plugin in two months from now or sooner.