[native] Create invitation modal

Summary:
After user clicks a link, we're going to call link verification endpoint. Based on the result, we will navigate user to this modal.

Depends on D7522

Test Plan:
Open a link that:

• is valid => user should see two buttons, one for joining and one for canceling
• is invalid => user should see an error message
• points to a community where the user is a member => modal should not be displayed

Reviewers: bartek, kamil, inka

Reviewed By: bartek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7524