Update remoting to 2.31 in the Jenkins core. (#2628)

The change introduces one serious bugfix (JENKINS-39596) and a bunch of various diagnostics improvements.

Bugfixes:

* [JENKINS-39596](https://issues.jenkins-ci.org/browse/JENKINS-39596) -
Jenkins URL in `hudson.remoting.Engine` was always `null` since `3.0`.
It was causing connection failures of Jenkins JNLP agents when using Java Web Start.
([PR #131](https://github.com/jenkinsci/remoting/pull/131))
* [JENKINS-39617](https://issues.jenkins-ci.org/browse/JENKINS-39617) -
`hudson.remoting.Engine` was failing to establish connection if one of the URLs parameter in parameters was malformed.
([PR #131](https://github.com/jenkinsci/remoting/pull/131))

Improvements:

* [JENKINS-39150](https://issues.jenkins-ci.org/browse/JENKINS-39150) -
Add logic for dumping diagnostics across all the channels.
([PR #122](https://github.com/jenkinsci/remoting/pull/122), [PR #125](https://github.com/jenkinsci/remoting/pull/125))
* [JENKINS-39543](https://issues.jenkins-ci.org/browse/JENKINS-39543) -
Improve the caller/callee correlation diagnostics in thread dumps.
([PR #119](https://github.com/jenkinsci/remoting/pull/119))
* [JENKINS-39290](https://issues.jenkins-ci.org/browse/JENKINS-39290) -
Add the `org.jenkinsci.remoting.nio.NioChannelHub.disabled` flag for disabling NIO (mostly for debugging purposes).
([PR #123](https://github.com/jenkinsci/remoting/pull/123))
* [JENKINS-38692](https://issues.jenkins-ci.org/browse/JENKINS-38692) -
Add extra logging to help diagnosing `IOHub` Thread spikes.
([PR #116](https://github.com/jenkinsci/remoting/pull/116))
* [JENKINS-39289](https://issues.jenkins-ci.org/browse/JENKINS-39289) -
 When a proxy fails, report what caused the channel to go down.
([PR #128](https://github.com/jenkinsci/remoting/pull/128))