Add request header tutorial to how-to guides

[salonichf5]

Proposed changes

Write a clear and concise description that helps reviewers understand the purpose and impact of your changes. Use the
following format:

Problem: Users need a consolidated document for both request and response header modifiers

Solution: Updated existing response header modifier guide with request header modifier docs.

Testing: Testing using make watch

Please focus on (optional): If you any specific areas where you would like reviewers to focus their attention or provide
specific feedback, add them here.

Closes #2270

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

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please add a brief note that summarizes the change.

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.38%. Comparing base (71a6c5c) to head (05ed810).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2715   +/-   ##
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  Coverage   89.38%   89.38%           
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  Files         110      110           
  Lines       10913    10913           
  Branches       50       50           
=======================================
  Hits         9755     9755           
  Misses       1100     1100           
  Partials       58       58           

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[ADubhlaoich]

Made a lot of edit suggestions. Requesting changes so that the remaining sections are changed to fit the style of everything else (Remove informal language, add line breaks before headings, etc).

Since there are repeat steps for setting the headers application up, you can make setting it up its own section and refer back to it the second time- removes the redundancy, cuts down on the amount of text.

[ADubhlaoich]

Some more small things! LGTM.