[okhttp-gson] Add Support for OAuth Access Token Retry

Description

The OkHttp-gson Java library does not currently have support for automatic OAuth access token retry. This is a problem for developers using generated SDKs as they have to re-implement token retry logic manually for every SDK. Other libraries, such as volley, retrofit, and retrofit2, already have this functionality built-in. I would like to have this for okhttp-gson as well, using a similar approach.

Swagger-codegen version

2.2.X and 2.3.X

Swagger declaration file content or url

N/A

Command line used for generation

java -jar swagger-codegen-cli.jar io.swagger.codegen.SwaggerCodegen generate -i ./build/spec.yaml -l swagger -l java -c ./config/sdk-java-config.json -o ./generated-sdk-java

Steps to reproduce

N/A

Related issues/PRs

Suggest a fix/enhancement

I plan on submitting a PR myself by implementing a solution similar to the one used in the retrofit library: https://github.com/swagger-api/swagger-codegen/commit/69d956f16b6c18d6282b5bd0d408505cf1adb56a

Start with the okhttp-gson Java library generated by the documented swagger-codegen command, then compare the proposed approach with the referenced retrofit commit. Define the OAuth access-token retry behavior and verify that generated SDK users no longer need to re-implement token retry logic manually.