Adjust nginx agent backoff settings and revert request timeout

[bjee19]

Proposed changes

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.

Closes #3801

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.99%. Comparing base (13d2288) to head (7c4d029).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3820   +/-   ##
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  Coverage   86.99%   86.99%           
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  Files         128      128           
  Lines       16412    16412           
  Branches       62       62           
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  Hits        14278    14278           
- Misses       1958     1959    +1     
+ Partials      176      175    -1     

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[bjee19]

Regarding these settings:

initial_interval: .5s
max_interval: 1.5s
max_elapsed_time: 3s
randomization_factor: 0.5
multiplier: 1.5

You can read about them here: https://pkg.go.dev/github.com/cenkalti/backoff/v4#section-readme.

But from my understanding:

initial_interval is the first sleep duration before the first retry
max_interval is the maximum sleep duration between reties
max_elapsed_time is the maximum time its going to wait before getting out of the backoff wait
randomization_factor adds a jitter so each sleep isn't the same.
multiplier is how the "base" interval grows. Basically how much the sleep interval is increasing.

Also all the settings are set to their default except for max_interval and max_elapsed_time. I wanted the maximum wait time to be around 2-3 seconds, since most nginx workers should restart in < 1 seconds, meaning only the long-lived connections would be over 2-3 seconds.

This wait is used here: https://github.com/nginx/agent/blob/main/internal/resource/nginx_instance_operator.go#L144