Add initial messages sync on private CCN

[nesitor]

Problem: Private CCNs don't have the whole history of network messages, so it's impossible to run a private CRN.

Solution: Sync the initial messages required to be able to run a private CRN. Also add it into the private guide.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.60%. Comparing base (eb3b653) to head (e2e619d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #561   +/-   ##
=======================================
  Coverage   94.60%   94.60%           
=======================================
  Files          89       89           
  Lines        4724     4724           
  Branches      648      648           
=======================================
  Hits         4469     4469           
  Misses        233      233           
  Partials       22       22           

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