Add Telegram auth

[iamelevich]

This pull request will add Telegram Auth for Web App or with Login widget.

This is not OAuth2, but I need it for my telegram webapp, so I decided to integrate it inside pocketbase instead of adding new route, cause it can be useful for others I hope.

Please take a look. Still have some things to do:

• Update js-sdk to support telegram auth
• Update dart-sdk to support telegram auth
• Update documentation

[ganigeorgiev]

Sorry, I don't want to merge it.

If Telegram doesn't have OAuth2 api then this cannot be part of the core package. It will be just hard to maintain since I don't use Telegram and I can't provide support for it in case they decide to change their api(s).

You can structure it as server-side "plugin" and create a standalone Go package that accept core.App and use that to bind to the OnBeforeServe hook and others to register your custom endpoint(s).

Eventually in the future, we may also add support for Admin UI addons but for now this a low priority.

[iamelevich]

Created a plugin if someone need such functionality. https://github.com/iamelevich/pocketbase-plugin-telegram-auth