[chore] Improve usage/setup of metadata.yaml

[bogdandrutu]

Few miss-usages:

1. Using a type like "receiver" when a simple "pkg" can be used, see "receiverhelper";
2. Defining metadata.yaml without a generate statement, see "pdata";
3. Legacy files that no longer need to be generated, see "exporterhelpe" the generated_status;
4. Missing entry into the README.md to generate the documentation, see "pdata"

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.98%. Comparing base (abdfdc8) to head (301dfd6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12343      +/-   ##
==========================================
+ Coverage   91.96%   91.98%   +0.01%     
==========================================
  Files         468      468              
  Lines       25460    25455       -5     
==========================================
  Hits        23415    23415              
+ Misses       1639     1634       -5     
  Partials      406      406              

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