Alternative package installer support

• Breaking: Remove --pre on sources from generated requirements-mxdev.txt.
  Usually it is not needed any longer, at least with pip 23.x.
  This is a breaking change if you rely on the --pre option being present in the generated file.
  Now the --pre option should be added to pip install when the generated file is used.
  This change enables the use of the generated file with the alternative pip replacement uv.
  [jensens]

• Breaking: Drop official support for Python 3.7 (it is end of life).
  [jensens]

• Document mx.ini sections vcs setting.
  [jensens]