Adjust nginx agent backoff settings (#3820)

[bjee19]

Cherry-pick #3820

Problem: As a result to NGINX Agent adding a wait for nginx workers to reload before updating nginx configuration, any long-lived connections would result in an excessively long wait between updating nginx configurations. This cause delays in NGF and on NGINX Plus, could cause a dropping of traffic if there was a wait between updating the configuration and updating the NGINX Plus upstreams.

Solution: Adjust the NGINX Agent reload configuration to lower the maximum wait time. Reverted the test request timeout duration back to 10 seconds.

Testing: Ran the SnippetsFilter functional test a couple of times and verified when there was a long-lived connection blocking on of the test cases, it went from a 27 second timeout -> 3 second. Also deployed nginx and verified the agent configuration was in there.

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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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.96%. Comparing base (7607c01) to head (bd82a9a).
⚠️ Report is 1 commits behind head on release-2.1.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-2.1    #3828      +/-   ##
===============================================
- Coverage        86.97%   86.96%   -0.02%     
===============================================
  Files              128      128              
  Lines            16001    16001              
  Branches            62       62              
===============================================
- Hits             13917    13915       -2     
- Misses            1918     1919       +1     
- Partials           166      167       +1     

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