Add Typesafe Config object as optional third arg

[petterarvidsson]

• Extend the plugin loading code to accept also methods annotated with PluginConstructor that as a optional third argument takes a Typesafe Config object

[petterarvidsson]

@nsg This adds the possibility for a Plugin to get its entire config as an optional third argument to the plugin constructor method (the one that returns Props). I will update forest and flowers as examples.

[nsg]

@petterarvidsson I like it, easier (for me) to understand, so I like it!

[petterarvidsson]

Usage examples: https://github.com/konstructs/server-plugin-flowers/pull/9 https://github.com/konstructs/server-plugin-forest/pull/14

[nsg]

@petterarvidsson yup, it was mainly these examples I was referring to :)