[Issue] New user join event not received in large groups

[J-Rios]

Context

Seems that current Bot didn't receive any new user join event in groups with more than 10k members...

From Telegram Bot API 5.2:

⚠️ WARNING! ⚠️ Service messages about non-bot users joining the chat will be soon removed from large groups. We recommend using the “chat_member” update as a replacement.

To-Do

1. Update Bot requeriment to use python-telegram-bot v13.5 (it include Bot API 5.2 full support).
2. Update Bot code to support the new python-telegram-bot version and new "chat_member" update to detect new members joins.
3. Check if nothing is broken after this changes.

[J-Rios]

python-telegram-bot v12 to v13 migration guide

https://github.com/python-telegram-bot/python-telegram-bot/wiki/Transition-guide-to-Version-13.0

List of deprecations and break changes:

• use_context now defaults to true (we already use it as true).
• python <=3.5 deprecated and unsupported (lets update Readme file regarding this).
• Message objects no longer have a "default_quote" attribute (we didn't use this).
• "@run_async" decorator unsupported (lets change this and use new "run_async=True" in Handler setup methods instead)
• Persistence of Bots (I think didn't affect us?).
• "**kwargs" argument removed from methods and changed to "api_kwargs" argument (lets check and replace if we use a custom argument).
• JobQueue Refactored (didn't affect us, we don't use JobQueue).
• Handling of time zones (didn't affect us, we don't pass time-zones).
• Changes in advanced scheduling (didn't affect us, we don't use Job or JobQueue).
• Rich Comparison (didn't affect us, we just compare specific things).
• Refactoring of Filters (we need to change and use new Filters objects).
• Updater "set_webhook()" deprecated (didn't affect us, we already use "start_webhook()").

[J-Rios]

Changes done in this commit.

Still we need to check if this changes breaks something (like poll mode, button mode) and check if it works ok in every type of groups (private groups, public groups, supergroups, large groups, etc)...

[J-Rios]

Seems everything is ok.

Closing.