Stop using libs-release

This commit makes sure we narrow down dependencies of the Spring
Framework to only Maven central. Optional dependencies that are not
available on Maven Central are now served from a more specific
repository (`ext-release-local`).

Closes gh-23124

Author: snicoll

build.gradle

@@ -116,7 +116,7 @@ configure(allprojects.findAll { (it.name != "framework-bom") } ) { project ->
 
 	repositories {
 		mavenCentral()
-		maven { url "https://repo.spring.io/libs-release" }
+		maven { url "https://repo.spring.io/ext-release-local" } // WebSphere uow
 		maven { url "https://repo.spring.io/milestone" } // Reactor
 		maven { url "https://oss.jfrog.org/artifactory/libs-snapshot" } // RSocket
 		mavenLocal()