v7.0.0

This is a major release only because of a minor ngclient API tweak: there
are no large functional changes.

Fixed

• Fix GHSA-qp9x-wp8f-qgjj:
  Incorrect delegation path matching on Windows
• Various documentation fixes (#2812, #2922, #2923)

Changed

• ngclient: Updater() now requires the named bootstrap argument to make it
  clearer that providing one is strongly recommended: previous default
  functionality can be reproduced with bootstrap=None (#2903)
• Prepare for removal of securesystemslib.hash (#2815)