Improved env var interpolation

[YassinEldeeb]

Interpolation Progress

• Eliminate the need for a EnvVarsFetcher abstraction, in favor of closures as a second argument to load_config.
• Correct the regex pattern to function properly
• Implement escaping of dollar signs using backslashes for literal dollar sign interpretation in configuration files.
• Support default values in environment variable interpolation syntax to provide fallbacks when variables are not set.
• Prioritize explicit environment variable values over provided default values.
• Full unit test coverage to verify proper handling of all common scenarios.
• Update documentation.
• Removed lazy_static dependency, since we don't really need it, we copy over the variables anyways.

Better Interpolation Logging

• Initialize the logger subscriber before config file parsing with info as the default level, then modify the log-level afterwards
• Flip all println!(...) before logger subscriber initialization including the config parser's code into using info!, error! and warning!

[github-actions]

💻 Website Preview

The latest changes are available as preview in: https://d2154a0a.conductor-t2.pages.dev

[github-actions]

✅ Benchmark Results

     data_received..................: 210 MB  2.6 MB/s
     data_sent......................: 652 MB  8.1 MB/s
     http_req_blocked...............: avg=2.81µs  min=611ns   med=1.45µs  max=34.87ms p(90)=1.94µs  p(95)=2.17µs 
     http_req_connecting............: avg=611ns   min=0s      med=0s      max=31.78ms p(90)=0s      p(95)=0s     
   ✓ http_req_duration..............: avg=4.31ms  min=59.5µs  med=2.32ms  max=76.69ms p(90)=11.19ms p(95)=15.54ms
       { expected_response:true }...: avg=4.31ms  min=59.5µs  med=2.32ms  max=76.69ms p(90)=11.19ms p(95)=15.54ms
   ✓ http_req_failed................: 0.00%   ✓ 0            ✗ 1654408
     http_req_receiving.............: avg=41.24µs min=6.48µs  med=15.92µs max=49.44ms p(90)=22.82µs p(95)=76.02µs
     http_req_sending...............: avg=15.78µs min=4.02µs  med=7.94µs  max=49.7ms  p(90)=10.8µs  p(95)=14.84µs
     http_req_tls_handshaking.......: avg=0s      min=0s      med=0s      max=0s      p(90)=0s      p(95)=0s     
     http_req_waiting...............: avg=4.25ms  min=41.32µs med=2.28ms  max=68.18ms p(90)=11.09ms p(95)=15.42ms
     http_reqs......................: 1654408 20680.020186/s
     iteration_duration.............: avg=4.41ms  min=99.76µs med=2.4ms   max=85.72ms p(90)=11.33ms p(95)=15.71ms
     iterations.....................: 1654408 20680.020186/s
     vus............................: 1       min=1          max=199  
     vus_max........................: 200     min=200        max=200  

[github-actions]

🐋 This PR was built and pushed to the following Docker images:

Docker Bake metadata

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