Add mention of knn_vector (#5979)

* Add  mention of `knn_vector`

Every other category explicitly mentions the actual type name in the "Field types and description" column except "k-NN vector" category that was missing the actual type name `knn_vector`

Signed-off-by: Ruben Laguna <ruben.laguna@gmail.com>

* Update _field-types/supported-field-types/index.md

Co-authored-by: kolchfa-aws <105444904+kolchfa-aws@users.noreply.github.com>
Signed-off-by: Ruben Laguna <ruben.laguna@gmail.com>

---------

Signed-off-by: Ruben Laguna <ruben.laguna@gmail.com>
Co-authored-by: kolchfa-aws <105444904+kolchfa-aws@users.noreply.github.com>

_field-types/supported-field-types/index.md

@@ -27,7 +27,7 @@ IP | [`ip`]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/ip/):
 [Autocomplete]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/autocomplete/) |[`completion`]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/completion/): Provides autocomplete functionality through a completion suggester.<br> [`search_as_you_type`]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/search-as-you-type/): Provides search-as-you-type functionality using both prefix and infix completion. 
 [Geographic]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/geographic/)| [`geo_point`]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/geo-point/): A geographic point.<br>[`geo_shape`]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/geo-shape/): A geographic shape.
 [Rank]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/rank/) | Boosts or decreases the relevance score of documents (`rank_feature`, `rank_features`).  
-[k-NN vector]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/knn-vector/) | Allows indexing a k-NN vector into OpenSearch and performing different kinds of k-NN search.
+k-NN vector | [`knn_vector`]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/knn-vector/): Allows indexing a k-NN vector into OpenSearch and performing different kinds of k-NN search.
 Percolator | [`percolator`]({{site.url}}{{site.baseurl}}/field-types/supported-field-types/percolator/): Specifies to treat this field as a query. 
 
 ## Arrays
@@ -187,4 +187,4 @@ The response contains documents 1 and 3 but not document 2 because only explicit
 ```
 
 The `_source` field still contains explicit `null` values because it is not affected by the `null_value`.
-{: .note}
+{: .note}