Support for postponing data transfer between agent and server

[pavolzibrita]

In some cases it is not easy to ensure or create connection between agent and server. It would be great if agent can log the data locally, the data could be later transferred were they can be processed (e.g. to s3), and then some other process could upload the data to the server.

So a data line like this: parca agent -> local disk -> move to s3 -> parca uploader (from s3 to server) -> parca server.

[brancz]

The parca server can handle out of order inserts just fine, so just creating a log from parca-agent would already be sufficient. I like this idea!