Add `.editorconfig` for consistent code style

[Frulfump]

Is your feature request related to a problem? Please describe.

Noticed while fixing akkadotnet/Akka.Management#3373 that the different .csproj there were using different indentation (tabs/spaces) and that a previous PR akkadotnet/Akka.Management#3370 had inconsistent indentation compared to the rest of the file.

Consistent code is easier to review (For me anything that appears out of the ordinary catches my eye and I then waste internal cycles)

Describe the solution you'd like

A basic .editorconfig to start with, setting some simple rules like indentation, charset, insert_final_newline, trim_trailing_whitespace, can always extend later with analyzer configuration etc

Describe alternatives you've considered
Don't think there really is any for this one

Additional context
Would open up for dotnet format usage and even dotnet format --verify-no-changes in CI to see that there are no regressions.

[Aaronontheweb]

@Frulfump I've dabbled with .editorconfig a bit myself and TBH I'm not super familiar with how to best use it, but I think it would be great to have one that at the very least enforces some consistent basic settings as you've described.

By all means, please go for it

[Aaronontheweb]

My ideal for a full-blown .editorconfig would be something that enforces ReSharper's default styles