Add prometheus monitoring to python app (open-telemetry#3004)

* Use OTEL exporter

* Fix errors

* Add requirements file in prometheus example directory

---------

Co-authored-by: Diego Hurtado <ocelotl@users.noreply.github.com>

docs/examples/metrics/prometheus-grafana/prometheus-monitor.py

@@ -0,0 +1,23 @@
+import random
+import time
+
+from prometheus_client import start_http_server
+
+from opentelemetry.exporter.prometheus import PrometheusMetricReader
+from opentelemetry.metrics import get_meter_provider, set_meter_provider
+from opentelemetry.sdk.metrics import MeterProvider
+
+# Start Prometheus client
+start_http_server(port=8000, addr="localhost")
+# Exporter to export metrics to Prometheus
+prefix = "MyAppPrefix"
+reader = PrometheusMetricReader(prefix)
+# Meter is responsible for creating and recording metrics
+set_meter_provider(MeterProvider(metric_readers=[reader]))
+meter = get_meter_provider().get_meter("view-name-change", "0.1.2")
+
+my_counter = meter.create_counter("my.counter")
+
+while 1:
+    my_counter.add(random.randint(1, 10))
+    time.sleep(random.random())

docs/examples/metrics/prometheus-grafana/requirements.txt

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+opentelemetry-exporter-prometheus==1.12.0rc1
+protobuf~=3.18.1