Adding Vietnamese as a new language (beta) (mattermost#24074)

* adding vietnamese

* ran npm run test:updatesnapshot

* ran npm run test:updatesnapshot

* Update i18n.jsx

* updatesed snapshot

* fix whitespace in snapshots

* add vi as supported server locale

* update docs to point at server-side list of supported locales

* removed incorrect translation

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Co-authored-by: Tom De Moor <tom@controlaltdieliet.be>
Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>