Add fallback/file buffering when requests can't be sent

[alsi-lawr]

Is your feature request related to a problem? Please describe.

When the specified OTLP endpoint is unreachable or otherwise incapable of receiving the request, it would be great to have support for a fallback to file (or a custom sink). This will ensure that no data loss would occur in the event of a failure to export, as this sink is being used in critical auditing infrastructure.

Proposal:

Change the IExporter interface for exports on log service requests to return some kind of information about the success/failure state of the exports. This can then feed into the sink to make a decision about whether to reroute the logs to a secondary sink (or keep it as a filesystem-only fallback), or to continue with ignoring the response. Expose an option to configure either a filesystem fallback location or a secondary sink fallback.

Edit: upon looking into it, we'd also need to catch exceptions in the case of unreachable grpc endpoints.

Describe alternatives you've considered

• Creating a resilient middleware that can receive the logs, however this still requires a network request.
• Overriding the implementations myself to ensure a fallback is present.

Additional context

I'd be happy to have a crack at implementing this for the filesystem-only approach if there's nothing already in the works.