Handle translations outside wiki/src WRT check_po: document or opt-out

Originally created by @hefee on #16103 (Redmine)

As part of the release process of our custom packages, we run check_po on PO files that come straight from Transifex. They don’t satisfy all these new requirements. So either the “Upgrade bundled binary Debian packages” section of wiki/src/contribute/release_process.mdwn must be adjusted to use your code that unifies PO headers, or there must be a way to opt-out of these new checks.

Feature Branch: https://0xacab.org/Hefee/tails/translation_platform_hooks

Parent Task: #15079 (closed)

Related issues

• Related to #16102 (closed)
• Related to #15819 (closed)
• Related to #11198