Do not fetch plugin-versions eagerly

https://github.com/jenkinsci/plugin-installation-manager-tool/blob/e71682ad1c8dd6977cf67f1a77f051af1ebe88cc/plugin-management-library/src/main/java/io/jenkins/tools/pluginmanager/impl/PluginManager.java#L794 looks like this file is retrieved even when it's not needed. This should be fixed to reduce bandwidth waste, every call is 10MB.

Start in plugin-management-library/src/main/java/io/jenkins/tools/pluginmanager/impl/PluginManager.java at line 794 and trace when plugin-versions is retrieved. Confirm which calls actually need that file and verify that unnecessary calls no longer fetch the 10 MB resource. The work is done when plugin-versions is fetched only when needed, without changing required plugin-management behavior.

Written by the indexing model from the issue text.