poc: shared loki source component

[kalleep]

PR Description

We have talked about having a shared library / functionallity for loki.source.*

Reason for this is that they all follow the same pattern but having their own implementation.

We usually have to fix deadlocks and other issues for each of these so having a shared implementation that they all can re-use makes it easier for us to test and fix issues for all of them.

Most component have either one or more sources, a source could be a file, server etc. So with something like this it should be possible to implement most of them using this kind of library, will probably have to adjust it a bit once we start to port component.

The shared component will start up a consume loop and a scheduling loop. Each implementation till pass a factory that will create sources (file, server etc).

They will all also use the same way of running targets and closing mechanism.

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated