Document error code 30011 & managed field for channels (discord#5867)

Author: panley01

docs/resources/Channel.md

@@ -24,6 +24,7 @@ Represents a guild or DM channel within Discord.
 | icon?                               | ?string                                                                     | icon hash of the group DM                                                                                                                                                                     |
 | owner_id?                           | snowflake                                                                   | id of the creator of the group DM or thread                                                                                                                                                   |
 | application_id?                     | snowflake                                                                   | application id of the group DM creator if it is bot-created                                                                                                                                   |
+| managed?                            | boolean                                                                     | for group DM channels: whether the channel is managed by an application via the `gdm.join` OAuth2 scope                                                                                      |
 | parent_id?                          | ?snowflake                                                                  | for guild channels: id of the parent category for a channel (each parent category can contain up to 50 channels), for threads: id of the text channel this thread was created                 |
 | last_pin_timestamp?                 | ?ISO8601 timestamp                                                          | when the last pinned message was pinned. This may be `null` in events such as `GUILD_CREATE` when a message is not pinned.                                                                    |
 | rtc_region?                         | ?string                                                                     | [voice region](#DOCS_RESOURCES_VOICE/voice-region-object) id for the voice channel, automatic when set to null                                                                                |

docs/resources/User.md

@@ -227,7 +227,7 @@ Create a new DM channel with a user. Returns a [DM channel](#DOCS_RESOURCES_CHAN
 
 ## Create Group DM % POST /users/@me/channels
 
-Create a new group DM channel with multiple users. Returns a [DM channel](#DOCS_RESOURCES_CHANNEL/channel-object) object. This endpoint was intended to be used with the now-deprecated GameBridge SDK. DMs created with this endpoint will not be shown in the Discord client. Fires a [Channel Create](#DOCS_TOPICS_GATEWAY_EVENTS/channel-create) Gateway event.
+Create a new group DM channel with multiple users. Returns a [DM channel](#DOCS_RESOURCES_CHANNEL/channel-object) object. This endpoint was intended to be used with the now-deprecated GameBridge SDK. Fires a [Channel Create](#DOCS_TOPICS_GATEWAY_EVENTS/channel-create) Gateway event.
 
 > warn
 > This endpoint is limited to 10 active group DMs.

docs/topics/Opcodes_and_Status_Codes.md

@@ -171,6 +171,7 @@ Along with the HTTP error code, our API can also return more detailed error code
 | 30007  | Maximum number of webhooks reached (10)                                                                                       |
 | 30008  | Maximum number of emojis reached                                                                                              |
 | 30010  | Maximum number of reactions reached (20)                                                                                      |
+| 30011  | Maximum number of group DMs reached (10)                                                                                      |
 | 30013  | Maximum number of guild channels reached (500)                                                                                |
 | 30015  | Maximum number of attachments in a message reached (10)                                                                       |
 | 30016  | Maximum number of invites reached (1000)                                                                                      |