Integrate CSS analysis from sonar-css (#2864)

Co-authored-by: vilchik.elena <[email protected]>

Author: yassin-kammoun-sonarsource

Diff for: .gitmodules

@@ -72,3 +72,6 @@
 	path = its/sources/javascript-test-sources
 	url = https://github.com/SonarSource/javascript-test-sources.git
 	ignore = untracked
+[submodule "its/css-sources/projects"]
+	path = its/css-sources/projects
+	url = https://github.com/SonarSource/css-test-sources

Diff for: css-sonarpedia/sonarpedia.json

@@ -0,0 +1,10 @@
+{
+  "rules-metadata-path": "sonar-javascript-plugin/src/main/resources/org/sonar/l10n/css/rules/css",
+  "languages": [
+    "CSS"
+  ],
+  "latest-update": "2021-03-02T17:22:27.244283200Z",
+  "options": {
+    "no-language-in-filenames": true
+  }
+}