Expose process version on the v3 API

[Gerg]

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• A short explanation of the proposed change:

Expose process versions on the v3 API.

• An explanation of the use cases your change solves

Process versions were already exposed on the v2 API in various places (e.g. GET /v2/apps. We did not bring this field over to v3.

I've historically been opposed to exposing process versions in v3, because they feel like an internal implementation detail of how CC and Diego stay in sync with eachother. That said, process versions are occasionally useful when locating LRPs in diego or debugging issues with the CAPI sync job. I've found myself using the v2 API to get process versions, which has demonstrated the value of bringing this forward to the v3 API.

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