fix(agent): Fix nr_header_create_distributed_trace_map mem leak when hashmap is destroyed

[zsistla]

This function created a new hashmap, but didn's pass the string dtor in so any strdupped values were not being freed when the hashmap was destroyed.

valgrind output from a multiverse run showed:

==220== by 0x6AA4680: nr_strdup (util_memory.c:156)
==220== by 0x6A83BD3: nr_header_create_distributed_trace_map (nr_header.c:60)
==220== by 0x6A45D28: nr_php_amqplib_retrieve_dt_headers (lib_php_amqplib.c:503)
==220== by 0x6A45D28: nr_rabbitmq_basic_get (lib_php_amqplib.c:742)
==220== by 0x6A74993: nr_zend_call_orig_execute_special (php_user_instrument.c:105)
==220== by 0x6A52EAA: nr_php_instrument_func_end (php_execute.c:2086)
==220== by 0x6A54D5B: nr_php_observer_fcall_end (php_execute.c:2188)
==220== by 0x71D7ED: zend_observer_fcall_end (in /usr/local/bin/php)
==220== by 0x6E79FF: execute_ex (in /usr/local/bin/php)
==220== by 0x6F0B42: zend_execute (in /usr/local/bin/php)
==220== by 0x67C06F: zend_execute_scripts (in /usr/local/bin/php)
==220== by 0x60FA3D: php_execute_script (in /usr/local/bin/php)

after applying the fix, valgrind had no issues.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	✅	8/8 passing
SOAK	✅	72/72 passing

[lavarou]

Nice find! Please add unit tests for nr_header_create_distributed_trace_map to axiom/tests/test_header.c.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.00%. Comparing base (b0184fd) to head (4de95b2).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1017   +/-   ##
=======================================
  Coverage   78.00%   78.00%           
=======================================
  Files         197      197           
  Lines       27424    27424           
=======================================
  Hits        21392    21392           
  Misses       6032     6032           

Flag	Coverage Δ
agent-for-php-7.2	78.15% <100.00%> (ø)
agent-for-php-7.3	78.17% <100.00%> (ø)
agent-for-php-7.4	77.88% <100.00%> (ø)
agent-for-php-8.0	77.24% <100.00%> (ø)
agent-for-php-8.1	77.74% <100.00%> (ø)
agent-for-php-8.2	77.35% <100.00%> (ø)
agent-for-php-8.3	77.35% <100.00%> (ø)
agent-for-php-8.4	77.37% <100.00%> (ø)

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[lavarou]

LGTM