Shared channels plugin APIs for MS Teams plugin (#25805)

New plugin APIs and hooks for accessing Shared Channels service via plugin. 

- RegisterPluginForSharedChannels(opts model.RegisterPluginOpts) (remoteID string, err error)
- UnregisterPluginForSharedChannels(pluginID string) error
- ShareChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
- UpdateSharedChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
- UnshareChannel(channelID string) (unshared bool, err error)
- UpdateSharedChannelCursor(channelID, remoteID string, cusror model.GetPostsSinceForSyncCursor) error
- SyncSharedChannel(channelID string) error
- InviteRemoteToChannel(channelID string, remoteID string, userID string) error
- UninviteRemoteFromChannel(channelID string, remoteID string) error

Hooks
- OnSharedChannelsSyncMsg(msg *model.SyncMsg, rc *model.RemoteCluster) (model.SyncResponse, error)
- OnSharedChannelsPing(rc *model.RemoteCluster) bool

server/public/plugin/api.go

@@ -32,7 +32,7 @@ type API interface {
 	// Minimum server version: 5.2
 	RegisterCommand(command *model.Command) error
 
-	// UnregisterCommand unregisters a command previously registered via RegisterCommand.
+	// UnregisterCommand unregisters a command previously register via RegisterCommand.
 	//
 	// @tag Command
 	// Minimum server version: 5.2
@@ -1207,6 +1207,73 @@ type API interface {
 	// @tag User
 	// Minimum server version: 9.3
 	UpdateUserAuth(userID string, userAuth *model.UserAuth) (*model.UserAuth, *model.AppError)
+
+	// RegisterPluginForSharedChannels registers the plugin as a `Remote` for SharedChannels.
+	// The plugin will receive synchronization messages via the `OnSharedChannelsSyncMsg` hook.
+	// This API is idempotent - when called repeatedly with the same `RegisterPluginOpts.PluginID`
+	// it will return the same remoteID.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	RegisterPluginForSharedChannels(opts model.RegisterPluginOpts) (remoteID string, err error)
+
+	// UnregisterPluginForSharedChannels unregisters the plugin as a `Remote` for SharedChannels.
+	// The plugin will no longer receive synchronization messages via the `OnSharedChannelsSyncMsg` hook.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	UnregisterPluginForSharedChannels(pluginID string) error
+
+	// ShareChannel marks a channel for sharing via shared channels. Note, this does not automatically
+	// invite any remote clusters to the channel - use `InviteRemote` to invite a remote , or this plugin,
+	// to the shared channel and start synchronization.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	ShareChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
+
+	// UpdateSharedChannel updates a shared channel. This can be used to change the share name,
+	// display name, purpose, header, etc.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	UpdateSharedChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
+
+	// UnshareChannel unmarks a channel for sharing. The channel will no longer be shared and
+	// all remotes will be uninvited to the channel.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	UnshareChannel(channelID string) (unshared bool, err error)
+
+	// UpdateSharedChannelCursor updates the cursor for the specified channel and RemoteID (passed by
+	// the plugin when registering).  This can be used to manually set the point of last sync, either
+	// forward to skip older posts, or backward to re-sync history.  This call by itself does not force
+	// a re-sync - a change to channel contents or a call to SyncSharedChannel are needed to force a sync.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	UpdateSharedChannelCursor(channelID, remoteID string, cusror model.GetPostsSinceForSyncCursor) error
+
+	// SyncSharedChannel forces a shared channel to send any changed content to all remotes.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	SyncSharedChannel(channelID string) error
+
+	// InviteRemoteToChannel invites a remote, or this plugin, as a target for synchronizing. Once invited, the
+	// remote will start to receive synchronization messages for any changed content in the specified channel.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	InviteRemoteToChannel(channelID string, remoteID string, userID string) error
+
+	// UninviteRemoteFromChannel uninvites a remote, or this plugin, such that it will stop receiving sychronization
+	// messages for the channel.
+	//
+	// @tag SharedChannels
+	// Minimum server version: 9.5
+	UninviteRemoteFromChannel(channelID string, remoteID string) error
 }
 
 var handshake = plugin.HandshakeConfig{