Add aliases for common item templates

[vlada-shubina]

Consider adding the alternative short names to some item templates, they are often misspelled.
Support for several short names is already available.

• gitignore - .gitignore
• globaljson - global.json
• editorconfig - .editorconfig
• nugetconfig - nuget.config

[vlada-shubina]

@baronfel how do you feel about it?

One note here: we should think of representation of those in list and help. While listing all possible short names is good for help, listing all possible short names in list tabular output might not be a good idea.

[baronfel]

I agree that unbounded choices could make the table look gnarly, but I think for this initial set we don't need to worry about it.