chore(daemon): modernize daemon codebase

[bduranleau-nr]

This PR aims to modernize the daemon codebase. It does this in four parts:

1. Run go fix ./... to automatically implement the fixes provided by Golang's fix tool.
2. Manually update the version of flatbuffers to the latest in go.mod and go.sum, remove legacy github protobuf dependency in favor of google.golang.org/protobuf.
3. Remove string_slice.go and replace the calls toStringSliceContains method with direct calls to slices.Contains.
4. Remove deprecated io/ioutil package (replaced by io and os packages).

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	✅	18/18 passing
SOAK	❌	133/135 passing

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.06%. Comparing base (18174dd) to head (7b97d00).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1195   +/-   ##
=======================================
  Coverage   80.05%   80.06%           
=======================================
  Files         189      189           
  Lines       27699    27699           
=======================================
+ Hits        22174    22176    +2     
+ Misses       5525     5523    -2     

Flag	Coverage Δ
agent-for-php-7.2	79.97% <ø> (ø)
agent-for-php-7.3	79.99% <ø> (?)
agent-for-php-7.4	79.86% <ø> (ø)
agent-for-php-8.0	79.45% <ø> (ø)
agent-for-php-8.1	79.67% <ø> (ø)
agent-for-php-8.2	79.27% <ø> (ø)
agent-for-php-8.3	79.35% <ø> (ø)
agent-for-php-8.4	79.37% <ø> (ø)
agent-for-php-8.5	78.68% <ø> (ø)

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