We want to support multiple versions of the fee extension, to allow new features while maintaining backward compatibility. This CL extends the framework and adds one new version, 0.11 (spec version 7), to the existing version 0.6 (spec version 3). A follow-on CL will add version 0.12 (spec version 8).
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127849044
