Reduce manifest.json debug log length

[ithinkandicode]

Logging the full manifest.json for every mod floods the logs, and always means the Godot console says "show less text".

This minor tweak changes it to log the contents as a single line instead.

There's also a const option (USE_EXTENDED_DEBUGLOG) to log the full contents, as it may still be helpful during development.

[Qubus0]

yea, that was necessary 👍

[ithinkandicode]

I'm providing support to a newbie modder and seeing the full JSON is actually quite helpful.

Perhaps we should enable the USE_EXTENDED_DEBUGLOG option by default