feat: CLI option to define output directory - #619

Just for your perusal, this may be related to https://github.com/openapi-generators/openapi-python-client/discussions/237 .

hey guys, I would like to have this too! do you need any help with this PR? this feature looks pretty straightforward

To be clear, the intended behavior is the same as if the user had switched into the passed output directory themselves (e.g., with cd) before running the command?

I want this option too because it's more comfortable to use output option instead switching of folder. Also it would be better to not create another folder in output folder during build

It would be nice to add the ability to generate the SDK directly into an existing folder

Example:

I have `sdk_folder`
Then run
$ openapi-python-client generate --path path/to/spec --output sdk_folder

Then I got `sdk_folder` with generated sdk instead of `sdk_folder/project_name`

It may also make sense to add the --overwrite-if-exists flag for this

This will be replaced by #1052