Deprecate CachingOperationInvoker#apply

This commit deprecates the only public accessor to
`CacheOperationInvoker` so that we can make the entire class package
private in the next feature release.

Closes gh-19089

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/invoker/cache/CachingOperationInvoker.java

@@ -111,7 +111,9 @@ private CachedResponse createCachedResponse(Object response, long accessTime) {
 	 * @param timeToLive the maximum time in milliseconds that a response can be cached
 	 * @return a caching version of the invoker or the original instance if caching is not
 	 * required
+	 * @deprecated as of 2.3.0 to make it package-private in 2.4
 	 */
+	@Deprecated
 	public static OperationInvoker apply(OperationInvoker invoker, long timeToLive) {
 		if (timeToLive > 0) {
 			return new CachingOperationInvoker(invoker, timeToLive);