Provide possibility of logging output generated from typegen to the console instead of interacting with the file-system

[MatthiasMargot]

This is necessary to support the following use-cases:

• appending the generated output to an already existing file
• funneling the output of this tool into further processing

One proposal is to add an optional flag which instructs the tool not to write the generated output to the file-system but to instead log it back to the console:

typegen input.json --log

# take the output and do something additional with it
# such as appending it to an already existing file
typegen input.json --log >> outpu.ts