Improve startup instructions

[samchang-msft]

When I tried to run locally, I ran into a few small issues that this PR should fix:

• the BACKEND1_PORT environment variable is output in the console instructions by local-setup.sh, but it's not added to the local config file
• in local-setup.sh the sed for {{ START_CMD_PY }} and {{ START_CMD_DOTNET }} wasn't replacing the variables properly, so the start up commands on the screen didn't make sense
• if I stopped the proxy server with Ctrl + C locally, the next run would fail to start up properly