Start experimenting with OpenTelemetry

This is meant to address
#2783, which began as
#2781

This is just an experiment, don't get too excited. The first impression
is that the OpenTelemetry API is really hard to work with, and the
concepts involved don't make a lot of sense. We (+@mkuratczyk) will
continue as soon as we have dealt with
#2785

Signed-off-by: Gerhard Lazu <gerhard@lazu.co.uk>

deps/rabbit/Makefile

@@ -132,14 +132,16 @@ APPS_DIR := $(CURDIR)/apps
 
 LOCAL_DEPS = sasl rabbitmq_prelaunch os_mon inets compiler public_key crypto ssl syntax_tools xmerl
 BUILD_DEPS = rabbitmq_cli syslog
-DEPS = cuttlefish ranch lager rabbit_common ra sysmon_handler stdout_formatter recon observer_cli osiris amqp10_common
+DEPS = cuttlefish ranch lager rabbit_common ra sysmon_handler stdout_formatter recon observer_cli osiris amqp10_common opentelemetry_api opentelemetry
 TEST_DEPS = rabbitmq_ct_helpers rabbitmq_ct_client_helpers amqp_client meck proper
 
 PLT_APPS += mnesia
 
 dep_cuttlefish = hex 2.4.1
 dep_syslog = git https://github.com/schlagert/syslog 3.4.5
 dep_osiris = git https://github.com/rabbitmq/osiris master
+dep_opentelemetry_api = hex 0.5.0
+dep_opentelemetry = hex 0.5.0
 
 define usage_xml_to_erl
 $(subst __,_,$(patsubst $(DOCS_DIR)/rabbitmq%.1.xml, src/rabbit_%_usage.erl, $(subst -,_,$(1))))

deps/rabbit/src/rabbit_channel.erl

@@ -45,6 +45,7 @@
 -include_lib("rabbit_common/include/rabbit_misc.hrl").
 
 -include("amqqueue.hrl").
+-include_lib("opentelemetry_api/include/otel_meter.hrl").
 
 -behaviour(gen_server2).
 
@@ -215,6 +216,8 @@
 -define(INCR_STATS(Type, Key, Inc, Measure),
         begin
             rabbit_core_metrics:channel_stats(Type, Measure, {self(), Key}, Inc),
+            % rabbit_log:warning("NOT FINE~nType: ~p~nMeasure: ~p~nSelf: ~p~nKey: ~p~nInc: ~p~n", [Type, Measure, self(), Key, Inc]),
+            ?otel_counter_add(lists:concat([Type, "_", Measure, "_total"]), Inc),
             %% Keys in the process dictionary are used to clean up the core metrics
             put({Type, Key}, none)
         end).