Fix javaagent download link (#153086)

## Summary

The URL we provide to download the Java agent from maven central is not
working as it used to.
This is exactly the same issue that was solved here:
elastic/apm-agent-java#3045 for more details.


### Checklist

This is just changing an URL in APM agent setup instructions

### Risk Matrix
This is just changing an URL in APM agent setup instructions, thus very
low risk

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/plugins/apm/common/tutorial/instructions/apm_agent_instructions.ts

@@ -400,7 +400,7 @@ export const createJavaAgentInstructions = (
 Do **not** add the agent as a dependency to your application.',
       values: {
         mavenCentralLink:
-          'http://search.maven.org/#search%7Cga%7C1%7Ca%3Aelastic-apm-agent',
+          'https://central.sonatype.com/search?q=g%253Aco.elastic.apm%2520a%253Aelastic-apm-agent&sort=published',
       },
     }),
   },