Output host_name property on configuration API endpoint

docs/api/apiv3/components/schemas/configuration_model.yml

@@ -19,6 +19,7 @@ example:
     userPreferences:
       href: "/api/v3/my_preferences"
   maximumAttachmentFileSize: 5242880
+  hostName: 'example.com:8080'
   perPageOptions:
     - 1
     - 10

docs/api/apiv3/tags/configuration.yml

@@ -20,4 +20,5 @@ description: |-
   | :-----------------------: | -------------------------------------------------- | ---------- | --------------------------------- | -------------------- |
   | maximumAttachmentFileSize | The maximum allowed size of an attachment in Bytes | Integer    |                                   | READ                 |
   | perPageOptions            | Page size steps to be offered in paginated list UI | Integer[]  |                                   | READ                 |
+  | hostName                  | The host name configured for the system            | String     |                                   | READ                 |
 name: Configuration

frontend/src/app/core/config/configuration.service.ts

@@ -118,6 +118,10 @@ export class ConfigurationService {
     return moment.localeData(I18n.locale).firstDayOfWeek();
   }
 
+  public get hostName():string {
+    return this.systemPreference('hostName');
+  }
+
   private loadConfiguration() {
     return this
       .apiV3Service

lib/api/v3/configuration/configuration_representer.rb

@@ -73,6 +73,12 @@ module API
                  },
                  render_nil: true
 
+        property :host_name,
+                 getter: ->(*) {
+                   Setting.host_name
+                 },
+                 render_nil: true
+
         property :user_preferences,
                  embedded: true,
                  exec_context: :decorator,