[BEAM-9551] Environment PB Pointer cleanup

[lostluck]

Go Protocol buffers strongly prefer to be pointers, and could cause issues otherwise WRT copying the proto's non-exposed state incorrectly. Likely hasn't caused any bugs, but it's a good practice to clean it up ASAP.

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---
XLang	---	---	---		---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

[lostluck]

Run Go Postcommit

[lostluck]

R: @youngoli

[youngoli]

Looks good to me. I'll have to keep in mind to prefer pointers with protos.