help: Improve user stream management docs.

Documents the procedure to subscribe / unsubscribe a user via their
profile and general stream settings.

Both methods are separated into tabs in the documentation.

Fixes #26902

help/manage-user-stream-subscriptions.md

@@ -23,6 +23,8 @@ other users to a stream][configure-invites].
 
 {start_tabs}
 
+{tab|via-stream-settings}
+
 {relative|stream|all}
 
 1. Select a stream.
@@ -33,6 +35,17 @@ other users to a stream][configure-invites].
 
 1. Click **Add**.
 
+{tab|via-user-profile}
+
+{!right-sidebar-view-profile.md!}
+
+1. Select the **Streams** tab.
+
+1. Under **Subscribe user to streams**, select a stream from the
+   dropdown list. You can start typing to filter streams.
+
+1. Click the **Subscribe** button.
+
 {end_tabs}
 
 {!automated-dm-stream-subscription.md!}
@@ -46,6 +59,21 @@ stream](/help/unsubscribe-from-a-stream).
 
 {start_tabs}
 
+{tab|via-stream-settings}
+
+{relative|stream|all}
+
+1. Select a stream.
+
+{!select-stream-view-subscribers.md!}
+
+1. Under **Subscribers**, find the user you would like
+   to remove from the stream.
+
+1. In the **Actions** column, click the **Unsubscribe** button in that row.
+
+{tab|via-user-profile}
+
 {!right-sidebar-view-profile.md!}
 
 1. Select the **Streams** tab.

zerver/lib/markdown/tabbed_sections.py

@@ -83,6 +83,7 @@ TAB_SECTION_LABELS = {
     "via-user-profile": "Via user profile",
     "via-organization-settings": "Via organization settings",
     "via-personal-settings": "Via personal settings",
+    "via-stream-settings": "Via stream settings",
     "default-subdomain": "Default subdomain",
     "custom-subdomain": "Custom subdomain",
     "zulip-cloud": "Zulip Cloud",