feat: add sample scripts for initializing MongoDB

[Taukon]

This PR adds sample scripts to initialize a MongoDB database for use with rtcstats-server.

• Install the MongoDB client module:

  npm install mongodb

• You can start a local MongoDB container with a command like the following:

  docker run -d \
    --name mongodb \
    -p 27017:27017 \
    -e MONGO_INITDB_ROOT_USERNAME=your_username \
    -e MONGO_INITDB_ROOT_PASSWORD=your_password \
    -v "$(pwd)/mongodb_db:/data/db" \
    --user "$(id -u):$(id -g)" \
    mongo