Optionally load ts config files

[nikolaik]

After #595 pulled inn @endemolshinegroup/cosmiconfig-typescript-loader we now transitively get the typescript dependency via ts-node in our project. This change increases node_modules size by ~57MB for module consumers, which seems a waste for everyone who are not running typescript. For us this ends up slowing down our CI runs by a small percent.

The proposed solution is to use the peerdependencyMeta field in package.json and declaring @endemolshinegroup/cosmiconfig-typescript-loader as an optional peer dependency. When configuring cosmicconfig, we detect if the dependency is installed using require.resolve and only then enable loading and setting up ts config files.

I'm pretty sure this would not make sense to handle downstream, since that project only works in a typescript context.

Would you consider a PR for this approach?

[dimaMachina]

Finally, it will be fixed by #1171 very soon!