Merge branch 'custom-emoji-docs' into 'master'

Add custom emoji doc

See merge request gitlab-org/gitlab!63381

doc/api/graphql/custom_emoji.md

+---
+stage: Plan
+group: Project Management
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+---
+
+# Use custom emojis with GraphQL **(FREE SELF)**
+
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/37911) in GitLab 13.6
+> - [Deployed behind a feature flag](../../user/feature_flags.md), disabled by default.
+> - Enabled on GitLab.com.
+> - Recommended for production use.
+> - To use in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-custom-emoji-api). **(FREE SELF)**
+
+This in-development feature might not be available for your use. There can be
+[risks when enabling features still in development](../../user/feature_flags.md#risks-when-enabling-features-still-in-development).
+Refer to this feature's version history for more details.
+
+To use custom emoji in comments and descriptions, you can add them to a group using the GraphQL API.
+
+Parameters:
+
+| Attribute    | Type           | Required               | Description                                                               |
+| :----------- | :------------- | :--------------------- | :------------------------------------------------------------------------ |
+| `group_path` | integer/string | **{check-circle}** Yes | ID or [URL-encoded path of the group](../index.md#namespaced-path-encoding) |
+| `name`       | string         | **{check-circle}** Yes | Name of the custom emoji.                                                 |
+| `file`       | string         | **{check-circle}** Yes | URL of the custom emoji image.                                            |
+
+## Create a custom emoji
+
+```graphql
+mutation CreateCustomEmoji($groupPath: ID!) {
+  createCustomEmoji(input: {groupPath: $groupPath, name: "party-parrot", file: "https://cultofthepartyparrot.com/parrots/hd/parrot.gif", external: true}) {
+    clientMutationId
+    name
+    errors
+  }
+}
+```
+
+After adding custom emoji to the group, members can use it in the same way as other emoji in the comments.
+
+## Get custom emoji for a group
+
+```graphql
+query GetCustomEmoji($groupPath: ID!) {
+  group(fullPath: $groupPath) {
+    id
+    customEmoji {
+      nodes {
+        name
+      }
+    }
+  }
+}
+```
+
+## Set up the GraphiQL explorer
+
+This procedure presents a substantive example that you can copy and paste into GraphiQL
+explorer. GraphiQL explorer is available for:
+
+- GitLab.com users at [https://gitlab.com/-/graphql-explorer](https://gitlab.com/-/graphql-explorer).
+- Self-managed users at `https://gitlab.example.com/-/graphql-explorer`.
+
+1. Copy the following code excerpt:
+
+  ```graphql
+      query GetCustomEmoji {
+        group(fullPath: "gitlab-org") {
+          id
+          customEmoji {
+            nodes {
+              name,
+              url
+            }
+          }
+        }
+      }
+  ```
+
+1. Open the [GraphiQL explorer tool](https://gitlab.com/-/graphql-explorer).
+1. Paste the `query` listed above into the left window of your GraphiQL explorer tool.
+1. Click Play to get the result shown here:
+
+![GraphiQL explore custom emoji query](img/custom_emoji_query_example.png)
+
+For more information on:
+
+- GraphQL specific entities, such as Fragments and Interfaces, see the official
+  [GraphQL documentation](https://graphql.org/learn/).
+- Individual attributes, see the [GraphQL API Resources](reference/index.md).
+
+## Enable or disable custom emoji API **(FREE SELF)**
+
+Custom emoji is under development and but ready for production use. It is
+deployed behind a feature flag that is **disabled by default**.
+[GitLab administrators with access to the GitLab Rails console](../../administration/feature_flags.md)
+can enable it.
+
+To enable it:
+
+```ruby
+Feature.enable(:custom_emoji)
+```
+
+To disable it:
+
+```ruby
+Feature.disable(:custom_emoji)
+```