Support for pushing logs to Azure Monitor in Linux scenarios

We have code that does this through ETW for Windows (see https://github.com/Azure/azure-functions-host/issues/2091) but we'll need an equivalent for Linux, similar to what we did for our system logs on linux (write to files, let the infrastructure ingest from those files).

Compare the existing Windows ETW implementation referenced in issue 2091 with the Linux system-log approach described here. Define the equivalent file-based path for Linux so infrastructure can ingest the logs into Azure Monitor, then verify that Linux log delivery works end to end.

Written by the indexing model from the issue text.