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

docs/reference/api/workspaces.md

@@ -177,6 +177,7 @@ of the template will be used.
                 ],
                 "subdomain": true,
                 "subdomain_name": "string",
+                "tooltip": "string",
                 "url": "string"
               }
             ],
@@ -466,6 +467,7 @@ curl -X GET http://coder-server:8080/api/v2/users/{user}/workspace/{workspacenam
                 ],
                 "subdomain": true,
                 "subdomain_name": "string",
+                "tooltip": "string",
                 "url": "string"
               }
             ],
@@ -780,6 +782,7 @@ of the template will be used.
                 ],
                 "subdomain": true,
                 "subdomain_name": "string",
+                "tooltip": "string",
                 "url": "string"
               }
             ],
@@ -1055,6 +1058,7 @@ curl -X GET http://coder-server:8080/api/v2/workspaces \
                     "statuses": [],
                     "subdomain": true,
                     "subdomain_name": "string",
+                    "tooltip": "string",
                     "url": "string"
                   }
                 ],
@@ -1345,6 +1349,7 @@ curl -X GET http://coder-server:8080/api/v2/workspaces/{workspace} \
                 ],
                 "subdomain": true,
                 "subdomain_name": "string",
+                "tooltip": "string",
                 "url": "string"
               }
             ],
@@ -1867,6 +1872,7 @@ curl -X PUT http://coder-server:8080/api/v2/workspaces/{workspace}/dormant \
                 ],
                 "subdomain": true,
                 "subdomain_name": "string",
+                "tooltip": "string",
                 "url": "string"
               }
             ],