Update data/control plane split design

[sjberman]

With the upcoming agent v3 release, the design for our control plane and data plane separation needs an update. Much of this is based off of discoveries from a recent PoC, as well as predicted design and implementation details that may be necessary. Added a new proposal that supersedes the old design.

Closes #2655

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.86%. Comparing base (5b38d8c) to head (5e8b715).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2729   +/-   ##
=======================================
  Coverage   89.86%   89.86%           
=======================================
  Files         107      107           
  Lines       10997    10997           
  Branches       50       50           
=======================================
  Hits         9883     9883           
  Misses       1054     1054           
  Partials       60       60           

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[salonichf5]

Looks good to me !