fix(rum): process the result of calling injector_end

[pablomartinezbernardo]

Changes in the internals for the injection library uncovered a bug where the result of calling injector_end were never considered.

This PR fixes that by

• Keeping behavior if injector_end doesn't result in injection
• Creating a new bucket brigade with a single bucket to override all the content of the response

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.70%. Comparing base (cdb3cb2) to head (c37b805).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #28   +/-   ##
=======================================
  Coverage   62.70%   62.70%           
=======================================
  Files           7        7           
  Lines         370      370           
  Branches       49       49           
=======================================
  Hits          232      232           
  Misses        100      100           
  Partials       38       38           

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