Merging loki-canary project into loki

cmd/loki-canary/Dockerfile

cmd/loki-canary/main.go

docs/canary/README.md

docs/canary/block.png

pkg/canary/comparator/comparator.go

pkg/canary/comparator/comparator_test.go

pkg/canary/reader/logproto.pb.go

pkg/canary/reader/reader.go

pkg/canary/writer/writer.go

production/ksonnet/loki-canary/config.libsonnet

production/ksonnet/loki-canary/jsonnetfile.json

production/ksonnet/loki-canary/loki-canary.libsonnet