Update "Using triplets" section in building-with-vcpkg documentation.

[Pravila00]

Fixes #2725

Changes

• Update existing links pointing to Vcpkg Triplets documentation.
• Replace the term "Custom triplets" by "Overlay triplets"

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.67%. Comparing base (497eaf4) to head (7903ac4). Report is 92 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2726      +/-   ##
==========================================
+ Coverage   87.12%   87.67%   +0.56%     
==========================================
  Files         200      190      -10     
  Lines        6109     5855     -254     
==========================================
- Hits         5322     5133     -189     
+ Misses        787      722      -65     

see 108 files with indirect coverage changes