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/queries/workspaceapps.sql

@@ -31,10 +31,11 @@ INSERT INTO
         display_order,
         hidden,
         open_in,
-        display_group
+        display_group,
+        tooltip
     )
 VALUES
-    ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, $17, $18, $19)
+    ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, $17, $18, $19, $20)
 ON CONFLICT (id) DO UPDATE SET
     display_name = EXCLUDED.display_name,
     icon = EXCLUDED.icon,
@@ -52,7 +53,8 @@ ON CONFLICT (id) DO UPDATE SET
     open_in = EXCLUDED.open_in,
     display_group = EXCLUDED.display_group,
     agent_id = EXCLUDED.agent_id,
-    slug = EXCLUDED.slug
+    slug = EXCLUDED.slug,
+    tooltip = EXCLUDED.tooltip
 RETURNING *;
 
 -- name: UpdateWorkspaceAppHealthByID :exec