concept from thesaurus as uri+label

these days catalogues move to capturing concepts (keywords) from thesauri using uri and label. how can I encode uri and label in a single pygeometa keyword property (the label is potentially multilingual)..

current:

```yaml
keywords:
wmo:
keywords:
en: [FOO,BAR]
```

suggested:

```yaml
keywords:
wmo:
- uri: example.com/foo
name: foo
- uri: example.com/bar
name:
en: bar
fr: bistro
```

For backwards compatibility, would be good to support both cases

An example is the [INSPIRE guideline on metadata](https://github.com/INSPIRE-MIF/technical-guidelines/blob/2022.2/metadata/metadata-iso19139/metadata-iso19139.adoc) to encode concept-from-thesaurus as

```xml

Meteorological geographical features

```

for backwards compatibility, would be good to support both cases

No implementation files or tests are named. Start by locating how the keywords property is parsed and rendered in pygeometa, then trace the existing dictionary form through its metadata outputs. Done means supporting both the current keyword lists and URI-plus-label entries, including multilingual labels, without breaking the existing form.

Written by the indexing model from the issue text.