feat(agent): Add RabbitMQ instrumentation using the php-amqplib library (#1009)

Most of the PR is basic instrumentation, retrieval of values and setting
attributes or creating metrics and is very similar to patterns we've
established in other instrumentation.
The DT header insertion logic is the trickiest bit since we are
modifying the headers in flight. (look to drupal and laravel for similar
logic).
Note: the DT header insertion logic, while trickiest, is something that
can be turned off anytime by the user by setting
newrelic.distributed_tracing_exclude_newrelic_header to true.


Initial commit does the following:
* Detect library via magic file
* Detect package and version information.
* Basic unit tests

Subsequent commits:
* Add attributes needed for rabbitMQ to message segment
* Instrument basic_publish and basic_get
* add unit tests, multiverse tests
* added support for PHP 7.x
* DT header insertion/retrieval
* Added more multiverse tests, especially around the DT functionality

Author: zsistla

agent/Makefile.frag

@@ -93,6 +93,7 @@ TEST_BINARIES = \
 	tests/test_internal_instrument \
 	tests/test_hash \
 	tests/test_lib_aws_sdk_php \
+        tests/test_lib_php_amqplib \
 	tests/test_memcached \
 	tests/test_mongodb \
 	tests/test_monolog \

agent/config.m4

@@ -231,7 +231,7 @@ if test "$PHP_NEWRELIC" = "yes"; then
   LIBRARIES="lib_aws_sdk_php.c lib_monolog.c lib_doctrine2.c lib_guzzle3.c \
   lib_guzzle4.c lib_guzzle6.c lib_guzzle_common.c \
   lib_mongodb.c lib_phpunit.c lib_predis.c lib_zend_http.c \
-  lib_composer.c"
+  lib_composer.c lib_php_amqplib.c"
   PHP_NEW_EXTENSION(newrelic, $FRAMEWORKS $LIBRARIES $NEWRELIC_AGENT, $ext_shared,, $(NEWRELIC_CFLAGS))
 
   PHP_SUBST(NEWRELIC_CFLAGS)

agent/fw_hooks.h

@@ -46,6 +46,7 @@ extern void nr_guzzle4_enable(TSRMLS_D);
 extern void nr_guzzle6_enable(TSRMLS_D);
 extern void nr_laminas_http_enable(TSRMLS_D);
 extern void nr_mongodb_enable(TSRMLS_D);
+extern void nr_php_amqplib_enable();
 extern void nr_phpunit_enable(TSRMLS_D);
 extern void nr_predis_enable(TSRMLS_D);
 extern void nr_zend_http_enable(TSRMLS_D);

agent/lib_aws_sdk_php.c

@@ -429,6 +429,12 @@ void nr_lib_aws_sdk_php_handle_version() {
   zval retval;
   int result = FAILURE;
 
+  /*
+   * The following block initializes nr_aws_sdk_version to the empty string.
+   * If it is able to extract the version, nr_aws_sdk_version is set to that.
+   * Nothing is needed in the catch block.
+   * The final return will either return a proper version or an empty string.
+   */
   result = zend_eval_string(
       "(function() {"
       "     $nr_aws_sdk_version = '';"