Start to implement code generation based on LINE OpenAPI specification

[Yang-33]

Some features(#283, #282, #255, #252, #251, #244, #232, #191) have not been implemented yet in the line-bot-sdk-ruby. The repository https://github.com/line/line-openapi publishes API schemas, which we could utilize by using the OpenAPI generator. This would allow SDK users to always access the latest features in the LINE API.

2.x version will contain tons of 💣 Breaking Changes 💣.

However, we plan to keep the 1.x code within 2.x, as we understand the challenges for SDK users to immediately transition from a 1.x library to a 2.x library.

[Yang-33]

(Memo: How to generate sdk in each repository)

• line-bot-sdk-java: It has custom generator. The generator's code is very short.
• line-bot-sdk-php: It doesn't have custom generator but it runs openapi-generator , and modify generated code by short script.
• line-bot-sdk-python: It has custom generator. The generator's code is a little bit long.

[4geru]

@Yang-33 @zenizh @mokuzon
Hello~. this is 4geru. I'm a LINE API Expert.
I'm interested in this issue.

I'd like to know how this issue is progressing.

[Yang-33]

Hello @4geru
Thank you for showing interest in our project. This task is currently assigned to our bot team member, @mokuzon. We are aiming to complete it within the next six months, but please understand that this is a goal rather than a guarantee.

We've also identified that a simple OpenAPI generator standard Ruby client does not meet the requirements for a bot SDK, which is why the initial PR was closed. There are currently over 40 requirements that need to be met for automatically generating the line-bot-sdk-ruby.

If you're interested in a bot SDK for Ruby that meets the latest Messaging API specifications, you can use https://github.com/line/line-openapi to create your own client. Alternatively, you're welcome to contribute to the issues in this repository. While we plan to phase out old code(= a code that is not generated by openapi generator) in 1-2 years, there's still plenty of opportunity for contributions in the meantime.

[Yang-33]

to @mokuzon

It seems like the goal is near.
I've created millstone for this task: https://github.com/line/line-bot-sdk-ruby/milestone/1 please check this.

and please resolve line/line-openapi#33 before releasing new version~

[Yang-33]

#337