The $@ option in bash doesn't make sense to come before `generate`
because the only option we can pass before generate cli usage is `help`.
System properties can be passed via JAVA_OPTS, so there's not really a
need for any intermediaries in the command line construction.
Having $@ at the end of the arguments list allows maintainers and users
inspecting options to quickly pass new options to a script. For example,
```
./bin/aspnetcore-petstore.sh --additional-properties sourceFolder=asdf
```
For command line arguments that may appear more than once in the
arguments list, this change doesn't provide any rules about overwriting
values that may exist (hard-coded) in the script. That is, in the
example above, if aspnetcore-petstore.sh already includes the
sourceFolder set to a different value, the "winning" value is up to the
options parser and openapi-generator-cli implementation.
