feat: add tooltip field to workspace app that renders as markdown (#19651)

In this pull request we're adding an optional `tooltip` field. The
`tooltip` field is a string field (with markdown support) that will be
used to display tooltips on hover over app buttons in a workspace
dashboard.

Tooltip screenshot

<img width="816" height="275" alt="Screenshot 2025-08-29 at 4 11 56 PM"
src="https://github.com/user-attachments/assets/52c736a1-f632-465b-89a0-35ca99bd367b"
/>

Tooltip video


https://github.com/user-attachments/assets/21806337-accc-4acf-b8c6-450c031d98f1

Issue: https://github.com/coder/coder/issues/18431
Related provider PR:
https://github.com/coder/terraform-provider-coder/pull/435

### Changes

- Added migration to add `tooltip` column to `workspace_apps` table
- Updated queries to get/set the new `tooltip` column
- Updated frontend to render tooltip as markdown (primary tool tip takes
precedence over template tooltip)

### Testing

- Added storybook test for `Applink` markdown rendering

coderd/database/dump.sql

@@ -2294,13 +2294,16 @@ CREATE TABLE workspace_apps (
     display_order integer DEFAULT 0 NOT NULL,
     hidden boolean DEFAULT false NOT NULL,
     open_in workspace_app_open_in DEFAULT 'slim-window'::workspace_app_open_in NOT NULL,
-    display_group text
+    display_group text,
+    tooltip character varying(2048) DEFAULT ''::character varying NOT NULL
 );
 
 COMMENT ON COLUMN workspace_apps.display_order IS 'Specifies the order in which to display agent app in user interfaces.';
 
 COMMENT ON COLUMN workspace_apps.hidden IS 'Determines if the app is not shown in user interfaces.';
 
+COMMENT ON COLUMN workspace_apps.tooltip IS 'Markdown text that is displayed when hovering over workspace apps.';
+
 CREATE TABLE workspace_build_parameters (
     workspace_build_id uuid NOT NULL,
     name text NOT NULL,