Add noise gates to cirq_google serialization

[dstrain115]

• This is a nice-to-have feature for cirq_google protos, since tests and simulations often use noisy circuits and these could be serialized as well.
• This would primarily be used for testing and storage since hardware does not (purposely) execute noise channels.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.70%. Comparing base (0df354c) to head (eac6377).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #7443    +/-   ##
========================================
  Coverage   98.70%   98.70%            
========================================
  Files        1114     1119     +5     
  Lines       98301    98461   +160     
========================================
+ Hits        97024    97184   +160     
  Misses       1277     1277            

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