[BUGFIX] Move doctrine initalization to connect() method

The event and custom type initalization of doctrine is moved
to an overwritten connect() method in the Connection class.

This prevents a premature establishment of a database connection
by calls to getDatabasePlatform().

This fixes the page unavailable during the connectToDB() in
the Frontend request handling.

Change-Id: Id6087002c7cbb9ed3938c4627d63b77515a7108f
Releases: master, 8.7
Resolves: #82795
Reviewed-on: https://review.typo3.org/54432


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>