feat: add Romansh as supported language (DEV-557) (#2053)

* fix docs

* add rm as supported language

Author: irinaschubert

docs/03-apis/api-admin/projects.md

@@ -67,6 +67,7 @@
 ```json
     {
       "shortname": "newproject",
+      "shortcode": "3333",
       "longname": "project longname",
       "description": [{"value": "project description", "language": "en"}],
       "keywords": ["test project"],

webapi/src/main/scala/org/knora/webapi/LanguageCodes.scala

@@ -13,11 +13,13 @@ object LanguageCodes {
   val EN: String = "en"
   val FR: String = "fr"
   val IT: String = "it"
+  val RM: String = "rm"
 
   val SupportedLanguageCodes: Set[String] = Set(
     DE,
     EN,
     FR,
-    IT
+    IT,
+    RM
   )
 }