Update Netty and OkHttp dependencies and resolve test failures (#3066)

This commit updates several dependencies in dependencies.gradle and resolves the resulting test failures:
- Netty: Updated strict upper bound from <4.2.0 to <5.0.0 (resolved to 4.2.14.Final).
- OkHttp: Removed strict upper bound of <5.0.0 and moved to dynamic versions section (resolved to 5.3.2).
- Cleaned up dependencies.gradle by moving strict dependencies (secretmanager, common-protos, gax) out of the dynamic versions section.
- Updated all gradle.lockfile files.

Resulting test fixes:
- Netty: Replaced NioEventLoopGroup with DefaultEventLoopGroup in NettyExtension and ProbingStepTest. In Netty 4.2+, LocalServerChannel no longer supports registration with NIO-backed event loops, throwing an IllegalArgumentException.
- OkHttp: Refactored ServiceMonitoringClient to safely handle empty responses using Optional.orElse(). In OkHttp 5.x, a 204 No Content response returns a non-null ResponseBody with an empty string, causing an assertion failure where MosApiException was incorrectly bypassed.

prober/src/test/java/google/registry/monitoring/blackbox/ProbingStepTest.java

@@ -34,11 +34,11 @@ import google.registry.networking.handler.NettyExtension;
 import io.netty.bootstrap.Bootstrap;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelHandler;
+import io.netty.channel.DefaultEventLoopGroup;
 import io.netty.channel.EventLoopGroup;
 import io.netty.channel.embedded.EmbeddedChannel;
 import io.netty.channel.local.LocalAddress;
 import io.netty.channel.local.LocalChannel;
-import io.netty.channel.nio.NioEventLoopGroup;
 import java.time.Duration;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.RegisterExtension;
@@ -58,7 +58,7 @@ class ProbingStepTest {
   private static final String TEST_MESSAGE = "TEST_MESSAGE";
   private static final String SECONDARY_TEST_MESSAGE = "SECONDARY_TEST_MESSAGE";
   private static final LocalAddress address = new LocalAddress(ADDRESS_NAME);
-  private final EventLoopGroup eventLoopGroup = new NioEventLoopGroup(1);
+  private final EventLoopGroup eventLoopGroup = new DefaultEventLoopGroup(1);
   private final Bootstrap bootstrap =
       new Bootstrap().group(eventLoopGroup).channel(LocalChannel.class);