IBX-2301: Added configuration to enable translations from i18n package

[mikadamczyk]

Question	Answer
JIRA issue	IBX-2301
Type	feature
Target Ibexa version	v4.0
BC breaks	no

Because i18n package will be added to the product there is a need to enable available translations on demand. This will prevent a bad user experience because of the lack of translations in the product. By default when a package with translations is installed, a language of a user interface is taken from browser settings, if a user doesn't choose his language under user settings. That is why a new setting is introduced.
To see translated strings in a product such configuration should be added.

ibexa:
    ui:
        translations:
            enabled: true

PR which adds new package to oss ibexa/oss#39

Checklist:

• Provided PR description.
• Tested the solution manually.
• Provided automated test coverage.
• Checked that target branch is set correctly (main for features, the oldest supported for bugs).
• Ran PHP CS Fixer for new PHP code (use $ composer fix-cs).
• Asked for a review (ping @ibexa/engineering).

[tomaszszopinski]

QA approved on IbexaDXP 4.0.x-dev. CI error is unrelated to this PR.