chore: Use `main` branch for mobile apps

[OmarIthawi]

Mobile apps uses a develop/main branching structure which is a deviation from the standard Open edX master/release/<release-name> branching model.

This issue is to discuss whether we use the develop or main branch to extract translations into Transifex.

[OmarIthawi]

cc: @volodymyr-chekyrta

[volodymyr-chekyrta]

New translations are adding to the dev branch with new features, so probably we can rely on the dev branch and then release strings and translations to the master branch.

[OmarIthawi]

Thanks @volodymyr-chekyrta. For now we're using the develop branch which should be sufficient for translators and developers at the moment.

I'm not suggesting a change to the branch model, but I've kept this issue here so it's not a code-only TODO.