[Bash] Support post form data

Created by: kevchentw

Before the fix, the bash client cannot handle post form data. After the fix, it can send post data.

Fix #4251 (closed)

example generated curl command

./client.sh --host http://localhost:3000 --dry-run loginForm  key:=123                                
curl -d 'key=123'     -X POST "http://localhost:3000/loginForm"

example yaml https://gist.github.com/kevchentw/9ab2df64c8ce8247a1edc607eed2843f

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