feat: add documentation provider

Author: xepozz

src/main/kotlin/com/github/xepozz/caddy/language/documentation/CaddyDirectiveDoc.kt

@@ -0,0 +1,8 @@
+package com.github.xepozz.caddy.language.documentation
+
+data class CaddyDirectiveDoc(
+    val name: String,
+    val description: String,
+    val syntax: String? = null,
+    val examples: String? = null
+)