python/iot3: make OTLP optional in simple API

[ymorin-orange]

Changes:

• Feature: allow using the simple API without OTLP

Closes: #236

---

How to test:

0. Pre-requisites:
   • a python 3.11 environment; if you do not have one already, use a container:

     $ docker container run \
         --detach \
         --name iot3 \
         --rm \
         -ti \
         --network host \
         -e http_proxy \
         -e https_proxy \
         -e no_proxy \
         --user $(id -u):$(id -u) \
         --mount type=bind,source=$(pwd),destination=$(pwd) \
         --workdir $(pwd) \
         python:3.11.9-slim-bookworm \
         /bin/bash -il
     $ docker container exec -u 0:0 iot3 apt update
     $ docker container exec -u 0:0 iot3 apt install -y git
     $ docker container attach iot3

     Note: in the following, the $ prompt means running in a shell that has access to python3.11, while the 🐍 $ prompt means running in the activated venv.
   • an OpenTelemetry collector on localhost:

     $ docker container run \
         --rm \
         -p 16686:16686 \
         -p 4318:4318 \
         jaegertracing/all-in-one:1.58

1. Install the IoT3 SDK package:

   $ python3.11 -m venv /tmp/iot3
   $ . /tmp/iot3/bin/activate
   🐍 $ pip install python/iot3

2. Run the IoT3 test-suite for the simple API:

   🐍 $ python/iot3/tests/test-iot3-core
   

---

Expected results:

1. The IoT3 SDK package is isntalled
2. The test-suite succeeds:
   • the test reports ([...] is a hex string):

     IoT3 Core SDK with MQTT and OTLP
     test/[...]/iot3/passed: b'passed'
     IoT3 Core SDK with MQTT and no OTLP
     test/[...]/iot3/no-otlp/passed: b'passed'
     

   • The Jaeger UI (on http://localhost:16686/) contains exactly three traces which MQTT topic (in Tags -> iot3.core.mqtt.topic) does not contain the no-otlp component:
     • one trace reports a failure due to not being connected;
     • one trace reports a publish;
     • one trace reports a receive with a reference to the publish, above.

[ymorin-orange]

The rust workflow fails for reasons unrelated to this PR, as no rust code was touched here.