Move RxGORM guide link to variable

Author: jamesfredley

grails-doc/build.gradle

@@ -190,6 +190,7 @@ publishGuideTask.configure { PublishGuideTask publish ->
                 'hibernate5Guide'          : hibernate5Guide,
                 'hibernate5GuideFromRef'    : '../' + hibernate5Guide,
                 'mongodb5Guide'            : '../grails-data/mongodb/manual/',
+                'rxGORMGuide'              : 'https://gorm.grails.org/7.3.4/rx/manual/', // last version released
                 'hibernate5Reference'      : 'https://docs.jboss.org/hibernate/orm/5.6/userguide/html_single/Hibernate_User_Guide.html',
                 'springbootapi'            : "https://docs.spring.io/spring-boot/${springBootVersion}/api/java/",
                 'springBootReference'      : "https://docs.spring.io/spring-boot/${springBootVersion}/reference/",

grails-doc/src/en/guide/async/rxjava/asyncRxGorm.adoc

@@ -17,7 +17,7 @@ specific language governing permissions and limitations
 under the License.
 ////
 
-https://gorm.grails.org/latest/rx/manual/[RxGORM] is new implementation of GORM that has the following goals:
+{rxGORMGuide}[RxGORM] is new implementation of GORM that has the following goals:
 
 * Reactive
 * Non-blocking
@@ -46,4 +46,4 @@ def show() {
 }
 ----
 
-For more information on how to use RxGORM, see the https://gorm.grails.org/latest/rx/manual/[RxGORM user guide].
+For more information on how to use RxGORM, see the {rxGORMGuide}[RxGORM user guide].