Add Sample ExpressJS App for testing (#2)

*Description of changes:*
Add Sample ExpressJS server with 3 endpoints:
- `curl http://localhost:8080/http`
- `curl http://localhost:8080/rolldice`
- `curl http://localhost:8080/aws-sdk-s3`

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sample-applications/simple-express-server/README.md

@@ -0,0 +1,29 @@
+## Sample Applications
+
+### Sample App Setup
+The Sample App is an ExpressJS Server that listens on `http://localhost:8080` by default
+You may change the port number from `8080` using:
+```
+export SAMPLE_APP_PORT=8082
+```
+
+To startup an Express Sample App without instrumentation
+```
+npm install
+node sample-app-express-server.js
+```
+
+To startup an Express Sample App with OTel auto-instrumentation
+```
+npm install
+npm install --save @opentelemetry/api
+npm install --save @opentelemetry/auto-instrumentations-node
+node --require '@opentelemetry/auto-instrumentations-node/register' sample-app-express-server.js
+```
+
+### Ping Sample App
+```
+curl http://localhost:8080/rolldice
+curl http://localhost:8080/http
+curl http://localhost:8080/aws-sdk
+```