[bash] Fix issue where paste command doesn't work on Mac

[Fryguy]

On a Mac, the paste commands end up producing error messages in subcommand help (as well as other places where paste is used). This PR fixes that by specifying - for STDIN which is compatible with both BSD and GNU paste.

Before:

~/dev/openapi-generator/samples/client/petstore/bash $ bash ./petstore-cli createUser --help

usage: paste [-s] [-d delimiters] file ...

usage: paste [-s] [-d delimiters] file ...

Parameters
usage: paste [-s] [-d delimiters] file ...


Responses
usage: paste [-s] [-d delimiters] file ...

After:

~/dev/openapi-generator/samples/client/petstore/bash $ bash ./petstore-cli createUser --help

createUser - Create user

This can only be done by the logged in user.

Parameters
  * body [] (required) - Created user object


Responses
  0  successful operation

@frol @bkryza @kenjones-cisco

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• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
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[Fryguy]

I also noticed that there is a second client.sh and _client.sh in the bash petstore sample project that doesn't belong there as it's not part of the generation. At some point, it seems the config was changed to include a scriptName, and at that time the client.sh and friends should have been deleted, but they weren't.

For this PR I didn't touch that file, but I'll create a separate PR that deletes the old client: #21987