feat(agent): Memcached instance metrics with host name

[ZNeumann]

These metrics can be used by the backend to create AWS relationship maps with memcached

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	✅	7/7 passing
SOAK	❌	55/56 passing

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.07843% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.53%. Comparing base (2321b9e) to head (6e720c9).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
agent/php_internal_instrument.c	94.28%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #958      +/-   ##
==========================================
+ Coverage   78.50%   78.53%   +0.03%     
==========================================
  Files         195      196       +1     
  Lines       27057    27108      +51     
==========================================
+ Hits        21241    21290      +49     
- Misses       5816     5818       +2     

Flag	Coverage Δ
agent-for-php-7.2	78.55% <96.07%> (+0.03%)	⬆️
agent-for-php-7.3	78.57% <96.07%> (+0.03%)	⬆️
agent-for-php-7.4	78.27% <96.07%> (+0.03%)	⬆️
agent-for-php-8.0	78.29% <95.91%> (+0.03%)	⬆️
agent-for-php-8.1	78.27% <95.91%> (+0.03%)	⬆️
agent-for-php-8.2	77.87% <95.91%> (+0.03%)	⬆️
agent-for-php-8.3	77.87% <95.91%> (+0.03%)	⬆️

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[lavarou]

Please address all comments and refactor the code.