Make APPLICATIONINSIGHTS_CONNECTION_STRING available to the child env (#7826)

Author: richardpark-msft

tools/stress-cluster/services/otelcollector/localtest.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+docker build -t oteltest .
+docker run -it \
+    -e ENV_FILE=/.env \
+    -v `pwd`/.env:/.env \
+    oteltest
+

tools/stress-cluster/services/otelcollector/startup.sh

@@ -3,4 +3,5 @@
 set -ex
 
 source $ENV_FILE
+export APPLICATIONINSIGHTS_CONNECTION_STRING
 /otelcol-contrib --config otel-collector-config.yml $@