ui.table_column link support for image columns

#### Is your feature request related to a problem? Please describe

Currently only text fields can have links
```
link: Indicates whether each cell in this column should be displayed as a clickable link. Applies to exactly one **text** column in the table.
```

#### Describe the solution you'd like

Tables can have images via Markdown. It would be nice to make an image column clickable.
Clicking on the image would appear in q.args and could be handled in the same way as for linked text columns.

Start by locating the ui.table_column implementation for linked text columns and the image-column rendering path. Trace how clicks are placed in q.args, then verify that clicking an image column produces the expected argument and can be handled like a linked text column.

Written by the indexing model from the issue text.