Studio: Translate Studio Assistant Welcome messages

[katinthehatsite]

Closes https://github.com/Automattic/dotcom-forge/issues/8279

Proposed Changes

This PR ensures that the welcome messages for which we have translated the strings in GlotPress are translated in Studio Assistant:

Testing Instructions

• Apply the following diff to your sandbox: D158963-code
• Sandbox the public API
• Pull the changes from this branch
• Switch the language to one of the supported languages e.g. Polish would be a good example as it has all the strings for welcome messages translated
• Start the app with npm start
• Navigate to the Assistant tab
• Confirm that the welcome messages are translated

Pre-merge Checklist

• [ ] Have you checked for TypeScript, React or other console errors?

[wojtekn]

Works as expected.