feat: workspaces

[nikkothari22]

Workspaces allows users to create multiple "spaces" each having it's own channels.

Example use case: a company like Frappe wants to run internal comms, customer support/community engagement etc all with just one Raven account and site. They would create private workspaces for internal comms or 1-on-1 customer engagement, and public workspaces for community engagement. This could apply to any organisation trying to separate departments/teams or using Raven to communicate with external vendors/staff.

DMs are not included in workspaces and hence are "shared".

Things to do:

Permissions

A new role of "Raven Admin" has been created - users with this role can create workspaces.

• Updated permission controller logic for Raven Channel, Raven Channel Member and Raven Message
• Permission controller logic for Raven Workspace and Raven Workspace Member
• Unit tests for all permission checks - in progress

Backend - APIs, Caching, Performance

• Fetching workspaces - in progress
• Unread count logic for workspaces
• Get Channel list API with workspace membership check for open channels
• Search API needs to only check for channel membership
• Validation - channels cannot be created without a workspace + channel ID needs to be name-spaced according to workspace (e.g. Workspace-my-channel instead of just my-channel
• Thread creation - copy over main channel workspace. If it's a DM channel, set is_dm_thread to 1.

Patches

• Added a new field is_dm_thread in Raven Channel for all threads created inside DMs. Since DMs do not have any workspace, threads created in a DM do not need a workspace.
• Patch to check is_dm_thread in all existing threads created in a DM
• Patch to migrate all existing users and channels to a default public workspace called "Raven". All existing Raven Users are members of this new workspace, and all of them are admins of this workspace.

UI

• Workspaces Sidebar layout
• Show unread count for workspaces
• Filter channel list in sidebar based on selected workspace
• Join workspace flow
• Create workspace flow
• Workspace List
• Workspace Member management
• Forwarding a message - show channel with workspace name
• Command Palette - show channels with workspace name
• Threads tab - only show threads from channels in the selected workspace
• Users can only mention channel in their own workspace

Other unrelated fixes in this PR:

1. Reactions now store the link to the channel. Deleting a channel will now delete all reactions in it. Closes Deleting a channel does not delete message reactions of messages in that channel #1151
2. List of channel members are now read from cache instead of database for better performance. Closes Cache channel membership data #762
3. Link previews are styled better. Closes Limit characters on link previews #1139

Closes #679