Enable autorefs plugin option to resolve closest references

The new version of the plugin will warn if there are multiple
references to the same object, for example:

```
WARNING -  mkdocs_autorefs: Multiple secondary URLs found for
  'frequenz.client.base.exception.ApiClientError.description':
  ['reference/frequenz/client/microgrid/#frequenz.client.microgrid.ApiClientError.description',
  'reference/frequenz/client/microgrid/#frequenz.client.microgrid.ClientNotConnected.description'].
```

To avoid this we enable the `resolve_closest` option:
https://mkdocstrings.github.io/autorefs/#non-unique-headings

But this looks like a bug in the plugin, so we'll see:
mkdocstrings/autorefs#52 (comment)

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

mkdocs.yml

@@ -87,6 +87,8 @@ markdown_extensions:
       permalink: "¤"
 
 plugins:
+  - autorefs:
+      resolve_closest: true
   - gen-files:
       scripts:
         - docs/_scripts/mkdocstrings_autoapi.py