File storage extension - Add test that validates filelogreceiver checkpoint storage

[djaglowski]

I want to see an end to end test. Create a log fie, collect part of it, shutdown the receiver, start it again, make sure it continued collection from the right place, nothing was missed, nothing collected twice. Again, no need to add to this PR, but I believe it is very important to have end to end tests like this.

Originally posted by @tigrannajaryan in #3087 (comment)