Add full support for OpenAPI specification version - `3.1.0`

[TharmiganK]

Description:

The Ballerina OpenAPI tool should support the latest OAS version - 3.1.0

Describe your problem(s)

This issue is created to check the OpenAPI tool compatibility with OAS version - 3.1.0.

Describe your solution(s)

• [ ] Check the unsupported changes in 3.1.0 and support it with the latest tool version.
• [ ] Design the tool with the compatible versions and issue warnings when unsupported OAS versions are provided rather than generating the incorrect code

Related Issues (optional): Discord connector uses the 3.1.0 version and encountered issues such as:

• https://github.com/ballerina-platform/ballerina-library/issues/6643

[TharmiganK]

[Copied from issue: https://github.com/ballerina-platform/ballerina-library/issues/5119]

There are several new features added from OpenAPI spec V 3.1. These features are not supported by our current Ballerina OpenAPI tool.

Summary of these new features are listed in this doc https://docs.google.com/document/d/1Y__2YvPmzOdL9Iexu-FciMkL80liuXZw1WRnAnHBKW8/edit?usp=sharing.

Please go though these features and try to integrate them to OpenAPI client/service generation