[PWA] Add Share Functionality

[Shailesh351]

This is 8th Feature of https://github.com/WideChat/Rocket.Chat/wiki/PWA-features to integrate PWA functionality in RC.

The goal of this PR is to add Share functionality to make RC on Mobile device to give similar experience as Native App.

Native Share demo from Viasat server because it need https

[engelgabriel]

I can understand the funtionality of SHARGING a channel or a message, and we will merge it, but I am not sure I understand what the sharing button does on the room list view bellow:

[Shailesh351]

@engelgabriel The sharing option in the room list is for sharing app with other people. It will contain link to direct message the logged in user. i.e. https://domain.com/direct/{myUsername}. So that new user will directly register and start chatting with me with that link

[CLAassistant]

All committers have signed the CLA.