Add remote_write use case

[valyala]

Prometheus provides the ability to replicate locally stored data to remote storage. This helps solving the following issues:

• Global query view, when you want running a query over data from multiple Prometheus instances.
• Long-term storage. Local storage size in Prometheus is limited by local disk capacity. Remote storage can provide higher data capacity via clustering and better compression.
• Scalability. Prometheus instance cannot automatically scale to multiple computers, while certain remote storage solutions can.

I'd recommend using single-node VictoriaMetrics for the use case because of the following features:

• It is easy to run - just a single binary with the minimum number of command-line flags to set up.
• It supports PromQL, so it can be used as drop-in replacement for Prometheus in Grafana dashboards.
• It is resource-efficient and provides good compression ratio for data.

[lucperkins]

@valyala I do think that doing something with the remote write API is a great idea, though I will likely expand the scenario to include multiple platforms

[roidelapluie]

While victoria supports PromQL it also support non-standard PromQL. I am unsure wether we should promote that kind of PromQL compatibility as it is just one direction.

[valyala]

While victoria supports PromQL it also support non-standard PromQL. I am unsure wether we should promote that kind of PromQL compatibility as it is just one direction.

There is no need in using non-standard PromQL when working with VictoriaMetrics. This is just extension, which can be used if needed.