Update release notes artifact verssions and URLs.

release_notes/voltha_2.12.rst
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  o Add urls for versioned docker, golang & pypi artifacts.
  o Updated ofagent-go
  o Updated pppoeagent
  o Updated votlha-protos
  o Note stale resources in the grid (~4yrs old) so they can be updated.

Change-Id: Idcf42112fb00ad597087d1150fe7f754960d749c
2 files changed