Implement local telemetry storage

Similar to how [az cli telemetry](https://github.com/Azure/azure-cli/blob/dev/src/azure-cli-telemetry/azure/cli/telemetry/__init__.py) and [dotnet cli telemetry](https://github.com/dotnet/sdk/blob/main/src/Cli/dotnet/Telemetry/Telemetry.cs#L137) works, we want to store telemetry events locally and have then uploaded by a background uploader. 

See also: #209 