Add additional allowed tags in untrusted notebook markdown (#150228)

This adds some extra allowed tags when rendering markdown in notebooks. Additions are:

```
  "b",

    "br",

    "caption",

    "center",

    "col",

    "colgroup",

    "details",

    "em",

    "font",

    "i",

    "kbd",

    "sub",

    "summary",

    "sup",

    "table",

    "tbody",

    "tfoot",

    "thead",

    "td",

    "th",

    "tr",

    "tt",

    "u",

    "video"
```