[BUGFIX] Prevent enforcing opened database connection with initCommands

This patch moves the execution of configured initCommands to the end
of connect function. This prevents a database connection from being
opened by default due to the execution of commands right after class
initialization and still ensures a connection is configured properly
before first command execution.

Furthermore this patch adds a new functional test for the ErrorHandler.
The test uses some predefined initCommands to enforce the strict mode
of MySQL database to be set. Due to the predefined initCommands the
test failed before as the connection was forced to be opened. For
further information see the referenced forge ticket.

Resolves: #83770
Releases: master, 8.7
Change-Id: I2287600959b3ec06d338e26373562850307ce0b1
Reviewed-on: https://review.typo3.org/55548


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Tested-by: Helmut Hummel <typo3@helhum.io>