[isabelle-dev] Towards the Isabelle2023 release

[Makarius]

We need to start thinking about the next official Isabelle release, approx. 10 
months after Isabelle2022 from 25-Oct-2022.

The current sketch for the schedule is as follows:

   Isabelle2023-RC0 06-Jun-2023
   Isabelle2023-RC1 04-Jul-2023
   ITP 2023 31-Jul..04-Aug-2023
   Isabelle2023 final 15-Aug-2023


I still have many small and big things to be finished --- in particular the 
new "isabelle build" for distributed / inhomogeneous compute clusters.


	Makarius