[contributing] `new-plugin.py` should use existing template file

[saygo-png]

Currently the script defines its own plugin template in a string. We already have a template as a nix file. Why not make the script simply copy over that file?

Right now we have to manually make sure these 2 templates are the same...
0754cdc

Pinging @khaneliman since this seems to be your creation.

[khaneliman]

Why not make the script simply copy over that file?

The benefit of the script, was just to pre-populate the file. If we update it to replaceVars the content of the template and copy it over, we could deduplicate it a bit.

[MattSturgeon]

This has come up in conversation before, although I can't find the relevant threads...

I agree, it'd be great to remove the duplication, and I've advocated for this in the past. But this shouldn't happen at the expense of the dynamic script being flexible or the static template being readable.