[Protobuf-Schema] Namespace updates

[Yurzel]

resolve #11114

Codegen

• fixed default packageName to openapitools
• api mustache packageName changed to {{packageName}}.{{apiPackage}}.{{classname}}
• package name changed to lowercase following the protobuf convention

[wing328]

Would "petstore.services.store_service" be a better package name?

If that's the case, then I think we should use the lambda.underscore instead of lambda.lowercase.

[Yurzel]

To be honest I don't even like to put "class name" into the package. The official documentations says this:

Packages
Package name should be in lowercase, and should correspond to the directory hierarchy. e.g., if a file is in my/package/, then the package name should be my.package.

There is also an another way(?) to keep the original package name and then use some kind of prefix/postfix to the Request/Response message itself. I'm scared of ugly code generated by protoc tho.

[wing328]

Thanks for the prompt reply and sorry that I forgot to mention why I think underscore should be used. It's based on this SO answer: https://stackoverflow.com/a/63228588/677735