resolves #1864 whatsapp_connector: deprecate legacy connector and clean up successor

[Fabilin]

This PR formally deprecates the whatsapp-connector module, and promotes the whatsapp-cloud-connector module as an alternative. It also does a cleanup pass on the latter, to make it more maintainable going forward.

The following changes have been made:

1. updated the README of both modules, as well as the relevant documentation pages
2. properly encapsulated WhatsApp API calls in the cloud connector
3. added missing endForWhatsAppCloud utility method
4. Split whatsAppCloudImage into one variant for images downloaded from a URL and another for images loaded in memory as a byte array
5. finished renaming Component to WhatsappTemplateComponent
6. moved the message preparation logic to the message classes
7. deprecated all message building methods in the legacy whatsapp-cloud connector