Develocity setup does not allow overwriting server url (elastic#122470) (elastic#122475)

This is a prerequisite to have
elastic#122296 passing in bwc
tests

Author: breskeby

build-tools-internal/src/main/groovy/elasticsearch.build-scan.gradle

@@ -28,7 +28,9 @@ develocity {
     // Automatically publish scans from Elasticsearch CI
     if (onCI) {
       publishing.onlyIf { true }
-      server = 'https://gradle-enterprise.elastic.co'
+      if(server.isPresent() == false) {
+        server = 'https://gradle-enterprise.elastic.co'
+      }
     } else if( server.isPresent() == false) {
       publishing.onlyIf { false }
     }