Exclamation marks are double escaped in upload-custom-translations

[garethbowen]

The translation files we export from POE and ship as default contain escaped exclamation marks, for example:

instance.upgrade.confirm.warning.text = This action cannot be undone, make sure your data has been backed up\!

On first run these are inserted into the database with _id messages-en and correctly unescaped, for example:

"instance.upgrade.confirm.warning.text": "This action cannot be undone, make sure your data has been backed up!",

If the files are uploaded through the admin UI the files are unescaped correctly.

However when I use upload-custom-translations the exclamation marks are double escaped and the backslash is rendered in the UI, for example:

"instance.upgrade.confirm.warning.text": "This action cannot be undone, make sure your data has been backed up\\!",

Reproduction

1. Navigate to cht-core/ddocs/medic/_attachments
2. Execute medic-conf --local upload-custom-translations replacing --local with the test instance as required.
3. Go to App Settings > Upgrade Instance
4. Pick a version and click "Upgrade" and wait for the dialog - don't submit the dialog!
5. Notice the dialog message is: "This action cannot be undone, make sure your data has been backed up!" (NB: the backslash just before the exclamation mark).

Expected

The message should be "This action cannot be undone, make sure your data has been backed up!"

Original noticed in medic/cht-core#5392

[garethbowen]

Ready for AT in 259-exclamation-mark-double-escaped

[ngaruko]

LGTM
before

Using medic-conf branch (local):