Document Draft SelectPlane confirmation behavior

[JacKane21]

Summary

• add Part DatumPlane to the documented Draft SelectPlane supported object list
• clarify that post-selection is confirmed by clicking an empty 3D View area

Context

• Upstream FreeCAD change: Draft: fix 2 issues with Draft_SelectPlane FreeCAD/FreeCAD#23333
• Related documentation issue: Draft Workbench: Adding Missing Information #27

Validation

• git diff --check -- wiki/Draft_SelectPlane.wikitext

Addresses part of #27.

[Reqrefusion]

Do not add T tags yourself; only modify the files in the wiki root directory, do not touch the translation files. Please check the latest version and ensure that the information you are adding has not been added previously. Also, be sure to cite the source of your change. Regression corrections should not be added to the documentation.

[JacKane21]

Thanks, I rechecked this PR as well. It only changes the root wiki file wiki/Draft_SelectPlane.wikitext, does not touch translation files or T tags, and I updated the PR body to list FreeCAD/FreeCAD#23333 as the source. The change documents the supported selection/confirmation behavior rather than a regression correction.