ITK 5.4.3 release checklist and status

[thewtex]

Release checklist and status:

• Check dashboard and CI
• Tag the ITK repository
• Bump ITK's version
• Update release branches
• Bump the ITKPythonPackage version
• Generate InsightToolkit and InsightData tarballs
• Archive testing data
• Write release notes
• Tarballs archived on ITKReleases NumFOCUS GDrive
• Generate Python packages and ITKPythonBuilds
• Update ITKSoftwareGuide
• Upload Python packages to PyPI
• conda-forge libitk package updated Regro cf autotick bot 5.4.3 h608595 conda-forge/libitk-feedstock#105
• Update versions in ITKRemoteModuleBuildTestPackageAction
• Publish GitHub Release
• Update downloads page
• Post on Discourse
• Post on Open Collective
• Post on Image.sc
• Post on Wordpress for itk.org entry