Using lazy_gettext in boot-time translations

[mesemus]

Description

This pull request fixes premature evaluation of i18n strings inside static fields. gettext call, that causes
the evaluation to be performed at boot time, was replaced with gettext_lazy that is performed at
request time. This fixes column labels in administration not being translated when language is changed.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
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• I've marked translation strings.
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[mesemus]

Please backport this change to RDM 12