Fix community centric bugs

[Behzad-rabiei]

• Update the API text to reflect when a user tries to connect an already connected platform.
• Leave the discord bot from the server if in the app we cannot add the user's platform.
• Leave the discord bot from the server when the community is deleted.
• Fix Role paginatation
• Fix user filed type in token model
• Remove selected channels to which bot has no access to (via migration script)