docs: add OEP-0058 - Translations Management

[Carlos-Muniz]

OEP-58

This PR introduces OEP-58 for Translations Management - Using the GitHub Transifex App and a separate repository containing translation files as a replacement for the edx-transifex-bot, and the current organizational structures used in the Transifex project edx-platform.

The proposal describes reasons for establishing this new process for managing our Translations by creating a new repository, placing all translation files in this repository, and using the Transifex Github App to manage the syncing of these Translation files as they are translated by the Open edX community.

Update:
A 3-part prototype was created for the openedx/credentials repository in the openedx/openedx-translations repository.

1. A GitHub action that generates English translation source files from the credentials repository, and adds them to the openedx-translations repository.
2. The transifex.yml file that allows for syncing the openedx-translations repository and an openedx-translations project in Transifex.
3. A CLI tool in openedx/openedx-atlas that can be used to pull translation files from openedx-translations back into a repository.