[chore] Update the Collector target audiences

[mx-psi]

Description

Reworks 'Target audiences' section to:

1. Reflect the three audiences we have today, distinguishing between component developers and Collector library users
2. Reflect that we encourage end-users to use the OpenTelemetry Collector Builder and that builder compatibility should be a concern when thinking about binary end-users

Link to tracking issue

Relates to #10004

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.33%. Comparing base (18e78af) to head (5da620e).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10539      +/-   ##
==========================================
- Coverage   92.39%   92.33%   -0.07%     
==========================================
  Files         393      393              
  Lines       18614    18647      +33     
==========================================
+ Hits        17199    17218      +19     
- Misses       1058     1069      +11     
- Partials      357      360       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.