Sidecar should start collectors when server is unavailable

[bernd]

Problem description

Starting the sidecar when the graylog server is unavailable doesn't start any collector processes, even if there are generated collector configs available locally.

Whether it makes sense to start collectors when the graylog server is down is debatable, of course. I think it is useful because some collectors are able to buffer messages if the graylog inputs are not available. Also, some collectors might not even send everything to graylog servers but also to other processes. Additionally, in the future there might be separate graylog ingest nodes which can be available while the API server is not.

The sidecar needs to cache the backend information locally to make this possible.

Steps to reproduce the problem

1. Configure collectors and assign the config to a sidecar
2. Start sidecar and wait until collectors are started
3. Stop graylog server
4. Stop sidecar
5. Start sidecar ➡️ no collectors will be started

Environment

• Sidecar Version: 1.0.0-alpha.1-SNAPSHOT (rev 3a319b0)