Add support for a --quiet flag for the spec command

[tsokalski]

The flask spec command currently always prints output to stdout. In cases where the output is being directed to a file, a --quiet command option (or similar) would be useful to pipe the results to the output file without printing them as well.

[Muzych]

About Flask Spec
the document said that you could add --output after flask spec command.
Such as flask spec --output openapi.json

[tsokalski]

About Flask Spec the document said that you could add --output after flask spec command. Such as flask spec --output openapi.json

Yeah, that's useful, but I'm looking to reduce output noise - my current spec is over 20k lines long, and printing the whole thing in a build pipeline while writing to a file is a bit distracting 😅.

I've opened #550 to achieve what I'm seeking.