docs: Prepare for new sub tree

See #11925

docs/content/en/functions/images/Gamma.md

@@ -1,36 +0,0 @@
----
-title: images.Gamma
-description: Returns an image filter that performs gamma correction on an image.
-categories: []
-keywords: []
-action:
-  aliases: []
-  related:
-    - functions/images/Filter
-    - methods/resource/Filter
-  returnType: images.filter
-  signatures: [images.Gamma GAMMA]
-toc: true
----
-
-The gamma value must be positive. A value greater than 1 lightens the image, while a value less than 1 darkens the image. The filter has no effect when the gamma value is 1.
-
-## Usage
-
-Create the filter:
-
-```go-html-template
-{{ $filter := images.Gamma 1.667 }}
-```
-
-{{% include "functions/images/_common/apply-image-filter.md" %}}
-
-## Example
-
-{{< img
-  src="images/examples/zion-national-park.jpg"
-  alt="Zion National Park"
-  filter="Gamma"
-  filterArgs="1.667"
-  example=true
->}}