[TASK] Use middleware for SOAP endpoint & remove pi-based plugin
This change adds a PSR-15 middleware to intercept all /ter and /ter?wsdl calls in favor of a pi-based plugin.
The plugin is removed (so the whole page in TYPO3 can be removed as well later-on).
The previous WSDL delivery endpoint extensions.typo3.org/typo3conf/ext/ter/tx_ter_wsdl.php is now a redirect to /ter?wsdl, so everything is covered by the middleware.