[Dev] Add a run directory when developing locally

[sean-breen]

Proposed changes

This change modifies the Makefile to create a build/run directory when running the make dev target, with the goal of making local development of the agent a little easier by keeping all of our runtime files in an easy to access location.

This directory must be added to the allowed_directories in nginx-agent.conf before running make dev.

allowed_directories:
  ...
  - <absolute path>/nginx-agent/build/run

This directory will contain several files which we create at runtime:

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.39%. Comparing base (db165d2) to head (aa01a6a).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1398      +/-   ##
==========================================
+ Coverage   86.27%   86.39%   +0.11%     
==========================================
  Files         102      102              
  Lines       12622    12622              
==========================================
+ Hits        10890    10905      +15     
+ Misses       1253     1236      -17     
- Partials      479      481       +2     

see 5 files with indirect coverage changes

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