Following Jan-Simon's suggestion, build-sdks-json.sh script must be rewritten to support any releases ("release//**")
See aborted review for more info:
More globally, this script must run each time xds-server startup (or triggered by an API of xds-server) in order to refresh SDKs list at any time.
To do that we need a way to easily retrieve list SDKs and detailed information of each SDKs. For now there is no way to find such information easily (time consuming > 2min and non robust implementation).