[WhatsApp Connector] add deprecation notices to the legacy WhatsApp connector

[Fabilin]

Due to the sunsetting of the WhatsApp on-premises API, we should deprecate the tock-bot-connector-whatsapp module in favor of the new tock-bot-connector-whatsapp-cloud. This also implies promoting the latter to a version type with more backward compatibility guarantees.

Open questions:

• should we declare the cloud connector as beta, or give it the same status as every other module?
• are there specific mechanisms that exist in the legacy whatsapp connector but are currently missing from the cloud connector?