WIP: Mapping Rules ADR

[agibsonccc]

What changes were proposed in this pull request?

This change proposes an ADR for declaring a set of transforms via protobuf allowing easier writing of op mappers for interop with different file formats.

(Please fill in changes proposed in this fix)

How was this patch tested?

(Please explain how this patch was tested. E.g. unit tests, integration tests, manual tests)

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