OONI Run v2: add support for separating versioning of copy (including translation) from nettests data

[hellais]

Currently if I go in and edit the translations of an OONI Run v2 descriptor or the copy it will bump the version number, triggering a notification saying the run link has changed.

This is a bit suboptimal as it will mean users that have installed an OONI Run v2 link will get spammed with notifications asking them to re-confirm it while the nettests haven't changed.

We discussed with @FedericoCeratto of splitting this out into two separate version numbers or potentially even having a different API for serving localization text that following a different versioning scheme. This would also allow sending updates to probe users for things like unreliable / broken tests etc.

cc @bassosimone @majakomel

[FedericoCeratto]

Summarizing the conversation we had:

• Probes fetch only the language desired
• Translations have an incremental version each. It increments when a given language is updated. It's stored in the probe.
• Translations version exist within ranges of the OONI Run descriptor version.

[FedericoCeratto]

Implemented in https://github.com/ooni/backend/pull/699

[FedericoCeratto]

1.0.63~pr700-112 deployed on prod (over 1.0.61~pr697-105)