api docs: Fix API documentation bugs issues with last commit.

* Actually bump API_FEATURE_LEVEL.
* Document changes in the endpoint documentation as well.
* Use standard linking/wording approach in API changelog.

templates/zerver/api/changelog.md

@@ -13,11 +13,11 @@ below features are supported.
 
 **Feature level 90**
 
-* We no longer include `sender_ids` in the `streams` section of
-  `UnreadMessagesResult`, which becomes the `unread_msgs` section of
-  the events that clients fetch when registering events at page
-  load time. (We don't believe this feature has ever been used in
-  a meaningful way.)
+* [`POST /register`](/api/register-queue): The `unread_msgs` section
+  of the response no longer includes `sender_ids` in the `streams`
+  dictionaries. These were removed because no clients were interested
+  in using the data, which required substantial complexity to
+  construct correctly.
 
 **Feature level 89**
 

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 = 89
+API_FEATURE_LEVEL = 90
 
 # 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

@@ -8857,6 +8857,10 @@ paths:
                               An array of dictionaries where each dictionary contains
                               details of all unread messages of a single subscribed stream,
                               including muted streams.
+
+                              **Changes**: Prior to Zulip 5.0 (feature level 90), the
+                              dictionaries included an additional `sender_ids` key listing
+                              the set of IDs of users who had sent the unread messages.
                             items:
                               type: object
                               description: |