FR: callout-metadata for admonition block

[efemkay]

using obsidian built in callout we can specify the callout-metadata by following syntax (as indicated by <metadata>)

> [!<type>|<metadata>]
> Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla et euismod nulla.

can we have similar feature when using admonition block. proposal would be like below, which the metadata text specified will be injected as a div attributes.

```ad-<type> # Admonition type. See below for a list of available types.
metadata:                  # specify any custom metadata

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla et euismod nulla.
```

the proposed div attributes would follow callout nomenclature e.g. below (where "metadata" is what we specify in admonition block's above)

<div data-callout="note" data-callout-metadata="metadata" data-callout-fold class="callout admonition admonition-note">