Adds yamllinting to Makefile.common

* adds yamllint target to Makefile.common for use by all Prometheus projects

Signed-off-by: Michal Wasilewski <mwasilewski@gmx.com>

.yamllint

@@ -0,0 +1,16 @@
+---
+extends: default
+
+rules:
+  braces:
+    max-spaces-inside: 1
+    level: error
+  brackets:
+    max-spaces-inside: 1
+    level: error
+  commas: disable
+  comments: disable
+  comments-indentation: disable
+  indentation:
+    spaces: consistent
+  line-length: disable

Makefile.common

@@ -118,7 +118,7 @@ endif
 %: common-% ;
 
 .PHONY: common-all
-common-all: precheck style check_license lint unused build test
+common-all: precheck style check_license lint yamllint unused build test
 
 .PHONY: common-style
 common-style:
@@ -198,6 +198,11 @@ else
 endif
 endif
 
+.PHONY: common-yamllint
+common-yamllint:
+	@echo ">> running yamllint on all YAML files in the repository"
+	yamllint .
+
 # For backward-compatibility.
 .PHONY: common-staticcheck
 common-staticcheck: lint