dotnet local tool support for NuGet

[xt0rted]

NuGet updates don't include dotnet local tools which are saved in .config/dotnet-tools.json (I believe this file can be placed anywhere, not just in the .config folder).

For now I'm working around this with a workflow that reads all the tools from that file and dispatches their info to another workflow that checks for updates and creates a PR if an update was found. It'd be great to not need this workaround though.

A demo of the workflows can be found in xt0rted/dotnet-tool-update-test.