fix: trim newlines from files reading by secrets

[jkroepke]

What this PR does / why we need it

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

• fixes oauth2.client.secret doesn't work when read from a file, but works when secret is passed plain-text #337

Special notes for your reviewer

Particularly user-facing changes

Checklist

Complete these before marking the PR as ready to review:

• DCO signed
• The PR title has a summary of the changes
• The PR body has a summary to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.04%. Comparing base (e0da4f2) to head (7499ffa).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #343      +/-   ##
==========================================
+ Coverage   81.80%   82.04%   +0.23%     
==========================================
  Files          51       51              
  Lines        3150     3152       +2     
==========================================
+ Hits         2577     2586       +9     
+ Misses        437      431       -6     
+ Partials      136      135       -1     

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