Restore the JetBrains plugin's Marketplace name

[holodorum]

Uploading the 0.3.0 plugin is rejected:

A plugin with the name KSON already exists on the Marketplace.
Please choose a unique name to avoid conflicts.

The cause is the IntelliJ Platform Gradle Plugin v2 migration. Under v1, pluginName set the archive name; under v2, pluginConfiguration.name sets <name> in plugin.xml. So pluginName = KSON silently overwrote the name and
undid the earlier fix for this exact collision.

The same shift is why the release doc pointed at KSON-[version].zip when the artifact is now jetbrains-[version].zip. Both are corrected here, along with the missing -Prelease=true on the documented build command — without it the
plugin builds as 0.3.0-SNAPSHOT.