[TASK] Doctrine: Migrate ImportantActions/SystemInformation

Change install tool "important actions" "system overview" to
list all configured database connections, the number of tables
per database and the number of tables mapped to a specific
connection.

Resolves: #77412
Releases: master
Change-Id: I235d2d56c6768060a4ce64dacfcb2f87e736d8f1
Reviewed-on: https://review.typo3.org/49406


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>