[Feature] Add an additional command line argument - "-format" to allow to output an expression instead of a singular version variable #3400
Description
Currently there is a -showvariable switch that allows us from command line to return a specific version variable.
By adding a new -format switch, we are able to customize the way the output looks like, allowing to combine several version variables and environment variables.
For example:
`dotnet gitversion -format "{Major}.{Minor}" will output only these 2 variables combined.