Add telemetry for /extensionList/ URL

[daniel-beck]

This adds a telemetry trial collecting information about the URLs accessed below /extensionList/. This is a fairly annoying endpoint, as it allows HTTP access to all sorts of @Extension annotated objects in a variety of ways, even if we might not want that.

We do that by no longer having Jenkins#getExtensionList(String) be @StaplerDispatchable, instead a new RootAction handles this, while reporting accesses to telemetry.

Additionally, two uses in core existed for /extensionList/… URLs:

• Functions#generateConsoleAnnotationScriptAndStylesheet (the ConsoleAnnotatorFactory part)
• MemoryUsageMonitorAction as shown on /systemInfo

These were migrated to new RootActions, whose urlName is a class name. TBD if that's nice or confusing, feedback welcome. Also, these might be temporary if the change turns out to be too complex to implement (so no adapting plugins to this change yet!).

Testing done

Manual test:

• http://localhost:8080/jenkins/manage/systemInfo still shows the monitor in the (unlinkable) tab.
• A freestyle job with https://plugins.jenkins.io/linenumbers/ https://plugins.jenkins.io/ansicolor/ https://plugins.jenkins.io/collapsing-console-sections/ and https://plugins.jenkins.io/timestamper/ produces the expected build log output. There's a JS error in linenumbers but that seems unrelated. Lots of calls to the new /hudson.console.ConsoleAnnotatorFactory, just one to /extensionList/hudson.console.ConsoleAnnotatorFactory/hudson.plugins.timestamper.annotator.TimestampAnnotatorFactory3/usersettings, as expected.
• Script console ExtensionList.lookupSingleton(jenkins.telemetry.impl.HttpExtensionList).createContent() shows output that would be sent to the telemetry endpoint.
• If usage statistics is enabled, script console ExtensionList.lookupSingleton(jenkins.telemetry.Telemetry.TelemetryReporter).doRun() submits data to the Uplink service.

Generated output format, excerpt:

Result: {"components":{"ace-editor":"1.1","ansicolor":"1.0.6", … ,"workflow-support":"946.v2a_79d8a_4b_e14"},"dispatches":{"hudson.console.ConsoleAnnotatorFactory/hudson.plugins.timestamper.annotator.TimestampAnnotatorFactory3":5}}

Proposed changelog entries

• Add telemetry to determine whether a specific URL (/extensionList/) is in use by plugins or can safely be removed in future releases of Jenkins.

Proposed changelog category

/label rfe

Proposed upgrade guidelines

N/A

Submitter checklist

• The Jira issue, if it exists, is well-described.
• The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood (see examples). Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during upgrade.
• There is automated testing or an explanation as to why this change has no tests.
• New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.
• New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO"), if applicable.
• New or substantially changed JavaScript is not defined inline and does not call eval to ease future introduction of Content Security Policy (CSP) directives (see documentation).
• For dependency updates, there are links to external changelogs and, if possible, full differentials.
• For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@mention

Before the changes are marked as ready-for-merge:

Maintainer checklist

• There are at least two (2) approvals for the pull request and no outstanding requests for change.
• Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
• Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
• Proper changelog labels are set so that the changelog can be generated automatically.
• If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
• If it would make sense to backport the change to LTS, a Jira issue must exist, be a Bug or Improvement, and be labeled as lts-candidate to be considered (see query).

[timja]

/label ready-for-merge

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This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!

[A1exKH]

LGTM.