api-docs: Document `away` as deprecated way to access presence_enabled.

Updates API documentation and changelog for user status `away`
now being a deprecated way to access a user's `presence_enabled`
setting for clients supporting older servers.

Final step in making user status `away` a deprecated way to access
`presence_enabled` for clients supporting older servers.

Part of transitioning from 'unavailable' user status feature to
'invisible mode' user presence feature.

templates/zerver/api/changelog.md

@@ -20,6 +20,15 @@ format used by the Zulip server that they are interacting with.
 
 ## Changes in Zulip 6.0
 
+**Feature level 148**
+
+* [`POST /users/me/status`](/api/update-status):
+  [`POST /register`](/api/register-queue), [`GET /events`](/api/get-events):
+  The user status `away` field/parameter is deprecated, and as of this
+  feature level are a legacy way to access the user's `presence_enabled`
+  setting, with `away = !presence_enabled`. To be removed in a future
+  release.
+
 **Feature level 147**
 
 * [`POST /streams/{stream_id}/delete_topic`](/api/delete-topic):

version.py

@@ -33,7 +33,7 @@ DESKTOP_WARNING_VERSION = "5.4.3"
 # Changes should be accompanied by documentation explaining what the
 # new level means in templates/zerver/api/changelog.md, as well as
 # "**Changes**" entries in the endpoint's documentation in `zulip.yaml`.
-API_FEATURE_LEVEL = 147
+API_FEATURE_LEVEL = 148
 
 # Bump the minor PROVISION_VERSION to indicate that folks should provision
 # only when going from an old version of the code to a newer version. Bump

zerver/openapi/zulip.yaml

@@ -1555,8 +1555,14 @@ paths:
                                         - user_status
                                 away:
                                   type: boolean
+                                  deprecated: true
                                   description: |
                                     Whether the user has marked themself "away" with this status.
+
+                                    **Changes**: Deprecated in Zulip 6.0 (feature level 148);
+                                    starting with that feature level, `away` is a legacy way to
+                                    access the user's `presence_enabled` setting, with
+                                    `away = !presence_enabled`. To be removed in a future release.
                                 status_text:
                                   type: string
                                   description: |
@@ -7172,11 +7178,17 @@ paths:
           example: on vacation
           required: false
         - name: away
+          deprecated: true
           schema:
             type: boolean
           in: query
           description: |
             Whether the user should be marked as "away".
+
+            **Changes**: Deprecated in Zulip 6.0 (feature level 148);
+            starting with that feature level, `away` is a legacy way to
+            access the user's `presence_enabled` setting, with
+            `away = !presence_enabled`. To be removed in a future release.
           example: true
           required: false
         - name: emoji_name
@@ -10373,8 +10385,14 @@ paths:
                           properties:
                             away:
                               type: boolean
+                              deprecated: true
                               description: |
                                 If present, the user has marked themself "away".
+
+                                **Changes**: Deprecated in Zulip 6.0 (feature level 148);
+                                starting with that feature level, `away` is a legacy way to
+                                access the user's `presence_enabled` setting, with
+                                `away = !presence_enabled`. To be removed in a future release.
                             status_text:
                               type: string
                               description: |