[FIXED JENKINS-38721, JENKINS-37282] - NPE in "CauseOfInterruption.UserInterruption" when user is missing (#2630)

* [FIXED JENKINS-38721] - Prevent NPE during rendering of "CauseOfInterruption.UserInterruption" when user is missing

It is a regression introduced in JENKINS-36594

* [JENKINS-38721] - Fix typo

Polish translations

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))

* Work around SUREFIRE-1226 just like https://github.com/jenkinsci/plugin-pom/pull/33.

* [JENKINS-39520] Implement ExtensionList.removeAll.

* @oleg-nenashev suggests not notifying listeners unless we are actually removing something.

* Add viewport meta tag

Enables better responsiveness on mobile devices

* fix: Use self-closing tag

* Remove minimum-scale for best accessibility

* Add viewport meta tag

[FIXED JENKINS-39604] - ResourceBundleUtil#getBundle() should report misses on the low level

Add @since on Util.isSafeToRedirectTo()

[FIXED JENKINS-39604] - ResourceBundleUtil#getBundle() should report resource misses on the low level

I propose the FINER level.

* [JENKINS-39465] - Tweak processing of enabled and disabled protocols in Jenkins instance

Due to whatever reason, without a definition of an array recipient field the data goes to the disk in the following way:

```
<enabledAgentProtocol>JNLP3-connect</enabledAgentProtocol>
<enabledAgentProtocol>JNLP4-connect</enabledAgentProtocol>
```

It is supposed to processed by Implicit array correctly, but it does not actually happen.
With a fix the data is being stored in another format:

```
  <enabledAgentProtocols>
    <string>JNLP3-connect</string>
    <string>JNLP4-connect</string>
  </enabledAgentProtocols>
```

This data now works correctly and gets deserialized correctly. readResolve() just adds a fallback for the case when Implicit array handling starts behaving correctly (?).

* [JENKINS-39465] - Add configuration roundtrip tests

* [JENKINS-39465] - Jenkins#agentProtocols cache must be invalidated when we reload the configuration

* [JENKINS-39465] - Remove obsolete comment from Tests

* Coarse fix for JENKINS-39555 - don't do the actions initialization by helper method

* Small cleanup of docs, import

* Testcase

* Review changes

* Changelog: Add the 2.29 release notice

* Fix the link

* Add some tests to  current behaviour of getLog method

* getLog(maxLines) reads only last maxLines lines now

It should speed up and reduce memory consumption for some plugins (i.e.
Email-ext Plugin).
Also now this method could be used to get last lines of build output in efficient manner.

* Fix issues from code review

[FIXED JENKINS-39454] Do not consider pendings when deciding whether a schedule result should be new or existing, as we have already taken a snapshot of actions. (#2609)

[FIXED JENKINS-38487] - Jenkins startup must not fail in the case of ComputerListener failure (#2610)

Without this code Jenkinbs startup fails if EnvInject fails to find global property file on startup.

Javadoc says "Exceptions will be recorded to the listener. Note that throwing an exception doesn't put the computer offline." regarding the listener method exception, hence we should not block Jenkins startup

[JENKINS-39414] Stapler 1.247

[FIXED JENKINS-39404] Restore symmetry by adding removeAction and removeActions methods to Actionable

[JENKINS-39404] Clarify the lack of transaction support and consequent effect on concurrent operations

- cannot use a local variable as the optimization only applies while we have not found the action being added

- We cannot modify `replaceAction` to return the dirty flag, in fact most callers probably don't care... but if you do care, we now provide `addOrReplaceAction`
- Clarify the javadocs to reflect that these methods are not going to affect actions added by transient action factories

[JENKINS-39404] We cannot change these to return a boolean, but doesn't matter because they would always return `true`