[ML] Add codeowner for docs screenshots (#123901)

This PR adds elastic/ml-ui as code owner for the ML specific bits of the screenshot_creation directory.

.github/CODEOWNERS

@@ -184,6 +184,8 @@
 /x-pack/test/functional_with_es_ssl/apps/ml/ @elastic/ml-ui
 /x-pack/test/alerting_api_integration/spaces_only/tests/alerting/ml_rule_types/ @elastic/ml-ui
 /x-pack/test/alerting_api_integration/spaces_only/tests/alerting/transform_rule_types/ @elastic/ml-ui
+/x-pack/test/screenshot_creation/apps/ml_docs @elastic/ml-ui
+/x-pack/test/screenshot_creation/services/ml_screenshots.ts @elastic/ml-ui
 
 # ML team owns and maintains the transform plugin despite it living in the Data management section.
 /x-pack/plugins/transform/  @elastic/ml-ui