[BUGFIX] Set default plugin title if no label was set

If the pluginTitle wasn't set, a warning message was rendered
in the page module as if the plugin wasn't configured.
We now use the PluginName as default to create
a visual difference between a plugin that is not configured.

Resolves: #99775
Releases: main, 12.4
Change-Id: Ic069edce5a74989ee32b2d40b1e645dc5449690d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79828


Tested-by: core-ci <typo3@b13.com>
Tested-by: Annett Jähnichen <mcmietz@web.de>
Reviewed-by: Annett Jähnichen <mcmietz@web.de>