[BUGFIX] Allow custom namespace in ExtbasePluginEnhancer

In Extbase, it is possible to configure a custom namespace for
plugin arguments:

plugin.tx_bennimack.view.pluginNamespace = bmack

This is now also respected in the Extbase Plugin Enhancer by omitting
"extension" and "plugin" properties and just using the "namespace"
property.

Resolves: #87005
Releases: master
Change-Id: I19c6338ec0d103837a5c5217ad7ba6643b6b6c54
Reviewed-on: https://review.typo3.org/58952
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jonas Eberle <flightvision@googlemail.com>
Tested-by: Jonas Eberle <flightvision@googlemail.com>
Reviewed-by: Aimeos <aimeos@aimeos.org>
Tested-by: Aimeos <aimeos@aimeos.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>