docs: document metadata access for go-templated cluster generator (ar…

…goproj#10929)

Signed-off-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com>

Signed-off-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com>
Signed-off-by: emirot <emirot.nolan@gmail.com>

docs/operator-manual/applicationset/GoTemplate.md

@@ -74,6 +74,13 @@ All your templates must replace parameters with GoTemplate Syntax:
 
 Example: `{{ some.value }}` becomes `{{ .some.value }}`
 
+### Cluster Generators
+
+By activating Go Templating, `{{ .metadata }}` becomes an object.
+
+- `{{ metadata.labels.my-label }}` becomes `{{ index .metadata.labels "my-label" }}`
+- `{{ metadata.annotations.my/annotation }}` becomes `{{ index .metadata.annotations "my/annotation" }}`
+
 ### Git Generators
 
 By activating Go Templating, `{{ .path }}` becomes an object. Therefore, some changes must be made to the Git