Support for local Docker builds

* add a git-ignored `local/` folder for Makefile/Dockerfile
* import `local/Makefile` to root Makefile
* add `.dockerignore`

.dockerignore

+.awcache
+.dockerignore
+.git
+.gitignore
+.github
+data*
+dist
+docker
+docs
+dump.rdb
+node_modules
+/local
+/tmp
+/vendor
+*.yml
+*.md
+/vendor
+/tmp

.gitignore

@@ -44,7 +44,9 @@ docker-compose.yaml
 /conf/provisioning/**/custom.yaml
 profile.cov
 /grafana
+/local
 .notouch
+/Makefile.local
 /pkg/cmd/grafana-cli/grafana-cli
 /pkg/cmd/grafana-server/grafana-server
 /pkg/cmd/grafana-server/debug

Makefile

+-include local/Makefile
+
 all: deps build
 
 deps-go: