docs: Revert peer port to 51235

[bthomee]

High Level Overview of Change

Following up on #5290, this change sets the [port_peer] back to the legacy port 51235 rather than to the default port 2459.

Context of Change

The config is part of the binary and, unless an explicit config is passed, the behavior of the binary will unexpectedly be different when the port changes. As the binary would then use a different port, it would possibly make the server inaccessible depending on how routes and firewalls are configured. To err on the safe side, this change restores the port to the legacy value as it was, but still recommends using the default port for new deployments.

Type of Change

• Documentation update

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.9%. Comparing base (01fc8f2) to head (6b71eb5).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5299   +/-   ##
=======================================
  Coverage     77.9%   77.9%           
=======================================
  Files          791     791           
  Lines        68006   68006           
  Branches      8352    8347    -5     
=======================================
+ Hits         52962   52968    +6     
+ Misses       15044   15038    -6     

see 2 files with indirect coverage changes

[legleux]

Bittersweet approval