[DOCS] Adds Data frame transforms subsection to the ML section (#38899)

This PR adds creating-df-kib.asciidoc and two screenshots to the repository and changes docs/ml/index.asciidoc.

docs/ml/creating-df-kib.asciidoc

@@ -0,0 +1,37 @@
+[[creating-df-kib]]
+== Creating {dataframe-transforms}
+
+beta[]
+
+You can create {stack-ov}/ml-dataframes.html[{dataframe-transforms}] in the 
+{kib} Machine Learning application.
+
+[role="screenshot"]
+image::ml/images/ml-definepivot.jpg["Defining a {dataframe} pivot"]
+
+Select the index pattern or saved search you want to transform. To pivot your 
+data, you must group the data by at least one field and apply at least one 
+aggregation. The {dataframe} pivot preview on the right side provides a visual 
+verification.
+
+Once you have created the pivot, add a job ID and define the index for the 
+transformed data (_target index_). If the target index does not exist, it will be 
+created automatically. You can optionally select to create a {kib} index pattern 
+for the target index. At the end of the process, a {dataframe} job is created as 
+a result. After you create {dataframe} jobs, you can start, stop, and delete them 
+and explore their progress and statistics from the jobs list.
+
+[role="screenshot"]
+image::ml/images/ml-jobid.jpg["Job ID and target index"]
+
+[NOTE]
+===============================
+If you want to use the {dataframe-transforms} feature, you must have the required 
+user roles and permissions:
+
+* `data_frame_transforms_user`: to get transforms and transforms stats,
+* `data_frame_transforms_admin`: to create/start/stop/delete transforms,
+* read permissions and `view_index_metadata` on the source indices,
+* index and read permissions on the target index (if the target index does not 
+exist, you need permission to create the index as well).
+===============================

docs/ml/index.asciidoc

@@ -72,4 +72,5 @@ For more information about {ml}, see
 
 include::creating-jobs.asciidoc[]
 include::job-tips.asciidoc[]
+include::creating-df-kib.asciidoc[]