Automate tx/rx to transifex

[sarathms]

Use github workflows to schedule/trigger pushing and pulling from Transifex.

Some reference implementations:
https://github.com/kobotoolbox/form-builder-translations/blob/master/.github/workflows/transifex-pull.yml
https://github.com/hanifbirgani/pep8ir/blob/main/.github/workflows/deploy.yml

• uses: https://github.com/stefanzweifel/git-auto-commit-action

[hellais]

Basically the problem is about:

1. Ensuring that when a new string is added to an app (Android, iOS or Desktop), you don't forget to update the csv and then the files in transifex.
2. Ensuring that when you make a release you have the latest version of the strings

As a first step we are going to just simplify the process for dealing with 1, but not requiring to manually download the CSV and as part of https://github.com/ooni/translations/blob/master/sync-csv-source.sh first fetch the master CSV from gsheets.

Some other approaches we discussed to address this better in the long term include:

• Adding a commit hook to do 1 and 2
• Doing 2 as part of some release script