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
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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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