Introduce examples dir with an autoinstrumented flask app (#168)

* Introduce examples dir with an autoinstrumented flask app

* Reword opentelemetry-bootstrap comment

* Add license header to the flask example

* Update examples/flask/Dockerfile

Author: xrmx

examples/flask/Dockerfile

@@ -0,0 +1,18 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+COPY . /app
+
+RUN pip install flask elastic-opentelemetry
+
+# Install all the instrumentations available for the installed packages
+RUN opentelemetry-bootstrap -a install
+
+# default flask run port
+EXPOSE 5000
+
+# Set some resource attributes to make our service recognizable
+ENV OTEL_RESOURCE_ATTRIBUTES="service.name=FlaskService,service.version=0.0.1,deployment.environment=development"
+
+CMD ["opentelemetry-instrument", "flask", "run"]

examples/flask/README.md

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+# Flask autoinstrumented application
+
+This is a barebone Flask app used for demonstrating autoinstrumentation with EDOT.
+
+You can build the application image it with:
+
+```
+docker build --load -t edot-flask:latest .
+```
+
+You can run the application with:
+
+```
+export OTEL_EXPORTER_OTLP_ENDPOINT=https://my-deployment.apm.us-west1.gcp.cloud.es.io
+export OTEL_EXPORTER_OTLP_HEADERS="Authorization=Bearer P....l"
+docker run -e OTEL_EXPORTER_OTLP_ENDPOINT="$OTEL_EXPORTER_OTLP_ENDPOINT" \
+  -e OTEL_EXPORTER_OTLP_HEADERS="$OTEL_EXPORTER_OTLP_HEADERS" \
+  -p 5000:5000 -it --rm edot-flask:latest
+```
+
+You can access the application from [http://127.0.0.1:5000](http://127.0.0.1:5000).

examples/flask/app.py

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+# Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+# or more contributor license agreements. See the NOTICE file distributed with
+# this work for additional information regarding copyright
+# ownership. Elasticsearch B.V. licenses this file to you under
+# the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from flask import Flask, jsonify
+
+app = Flask(__name__)
+
+
+@app.route("/", methods=["GET"])
+def home():
+    return jsonify(message="Hello, world!")