Update the documentation and git repo to point towards new translation portal on Crowdin

[sihma]

As of now:

• the old portal translate.erpnext.com has had an expired certificate since December 2023 (soon seven months)
• the new portal on Crowdin has received contributions and was announced in the community forum by the main dev (@barredterra) working on it
• there doesn't seem to be any intention to roll back to the old translation method, rather, new translations on Crowdin are planned to be brought to stable

I know it is a work in progress, but since translation takes so much time, isn't it better to get as many people onboard and going as soon as possible? I was highly interested in ERPNext, but I wanted to translate, and just the lack of documentation on why translate.erpnext.com was down for half a year was almost putting me away from it.

Here are the steps I'd see as important

• [ ] Redirect translate.erpnext.com to Crowdin portal
• [ ] Update docs:
  • [ ] Frappe Framework: 1, 2
  • [ ] ERPNext: 1, 2 (at the bottom)
  • [ ] Archive this repository

So much thanks for the work put into getting translation better!