Feature: #108776 - Allow to set user interface language when using CLI to create user 

See forge#108776

Description 

The CLI command backend:user:create now supports the option --language (or -l) to set the desired language for the user interface.

./bin/typo3 backend:user:create --language=de
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User creation using environment variables:

TYPO3_BE_USER_NAME=username \
TYPO3_BE_USER_EMAIL=admin@example.com \
TYPO3_BE_USER_GROUPS=<comma-separated-list-of-group-ids> \
TYPO3_BE_USER_LANGUAGE=de \
TYPO3_BE_USER_ADMIN=0 \
TYPO3_BE_USER_MAINTAINER=0 \
./bin/typo3 backend:user:create --no-interaction
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