[NEW] Change request to send message to use REST API

[rafaelks]

Description

Right now the app is using WebSocket to send message, we need to change to REST to have more reliability on what's going on. Requirements:

• It needs to send any kind of message we already support;
• Needs to handle failure responses in a clever way (leaving the message in failed state, allowing the user to retry it);
• Unit tests;

Blocked by RocketChat/Rocket.Chat#8864

[rafaelks]

@cardoso We can now support this feature with this new API: RocketChat/Rocket.Chat#8947.

We need to make a check and only use the REST in case server version is greater than 0.60.