Reduce log level on notice about optional extensions

[jglick]

Noticed an inconsistency in jenkinsci/kubernetes-credentials-plugin#20. Extends #2305 to better match ec61660 which uses FINE for optional extensions. If an extension is optional and it is not loaded, that is usually because the required plugin is missing, which is not interesting—do not clutter the log with it.

Proposed changelog entries

• By default suppress log message about a missing optional extension.

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[daniel-beck]

Did we ever resolve the bug which resulted in batch-installs of plugins not considering optional dependencies for install/load order? That would be made more difficult to diagnose with this message gone on regular instances. Which of two plugins implements an extension depending on the plugin is sometimes basically arbitrary, and in a few cases changed over time.

In general, this looks like a message appearing generally during startup, which is pretty cluttered anyway, and then only once per extension, so why not accept a little more log spam to address the cases in which the outcome is unexpected?

[jglick]

Did we ever resolve the bug which resulted in batch-installs of plugins not considering optional dependencies for install/load order?

No clue.

why not accept a little more log spam

To be clear, this patch is bringing this one case (arising from an obscure aspect of Guice behavior) in line with others of longer standing (including direct SezPoz loading). As seen in the linked PR, Jenkins already logged some optional extension failures at FINE, just not consistently. You can always turn on fine logging here if you suspect a Jenkins bug, but the expectation is that not loading an optional extension is quite normal and not worth mentioning.

[daniel-beck]

🤷‍♂ Easy enough to revert if necessary.

[oleg-nenashev]

Fine with me

[oleg-nenashev]

I plan to merge it tomorrow if no negative feedback