Disable externalDocumentationLinks unless a project property is set

I think these are causing lots of CI failures at the moment.

Signed-off-by: Graham <gpe@openrs2.dev>

build.gradle.kts

@@ -148,6 +148,7 @@ configure(subprojects.filter { it.isFree }) {
                     remoteLineSuffix.set("#L")
                 }
 
+                if (project.hasProperty("externalDocumentationLinks")) {
                     externalDocumentationLink {
                         url.set(URL("https://asm.ow2.io/javadoc/"))
                     }
@@ -218,6 +219,7 @@ configure(subprojects.filter { it.isFree }) {
                 }
             }
         }
+    }
 
     plugins.withType<JavaPlugin> {
         dependencies {