Add link to agent a stage is running on to stage summary

[Hammie]

Adds a line to the console view stage summary, showing which agent the stage is running on.

Fixes #426

Testing done

Ran the plugin on a Jenkins instance with multi-stage pipelines, and so far everything seems to work.

Submitter checklist

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[KalleOlaviNiemitalo]

What does this render if the pipeline has agent none and there is no agent for the stage either? We have some pipelines like that, where an agentless stage sets job properties conditionally before the job starts waiting for an available agent.

[timja]

What does this render if the pipeline has agent none and there is no agent for the stage either? We have some pipelines like that, where an agentless stage sets job properties conditionally before the job starts waiting for an available agent.

Good find, there's a bug it always displays the text when it should only do it if the agent is running on a stage:

[Hammie]

I've also been testing it on our production instance, and there are some more edge cases where it is not quite working as expected.

• A parallel stage copies the agent property from its first child stage
• A simple single-stage pipeline also shows no agent (even when already running)

I'll try and fix these and also write some tests for them so we can have some confidence in it working well.

But I'm not an experienced Java dev, so we'll see how that goes...

[Hammie]

I've added some tests and fixed the known issues.

Not really happy with the actual agent lookup code, but I don't think I can really do it better.

At the very least the tests should make it easier if someone wants to try and rewrite it.

[timja]

Code looks pretty good from a read, one improvement needed and I'll do a re-test when I get a chance

[timja]

The link I am currently getting when I click to view the agent is:
http://localhost:8085/jenkins/job/junit-attachments-test/job/master/31/pipeline-console/undefined/computer/(built-in)/

(with undefined in the url) and the link doesn't work

[timja]

Doesn't seem to be working the agent name is coming through as jenkins and not Jenkins:

[Hammie]

I guess jenkins is also fine. What does the link say? (built-in) or also jenkins?

[Hammie]

Problem was the capitalize css class applied to it.

[timja]

LGTM thanks for your work on this!