Move milestone templates

[MikeOpenHWGroup]

After completion of #592 and #593, the templates for our program milestones are located at Project-Descriptions-and-Plans/CV32E40Pv1/Milestone-data/templates. This is not a good location as these templates are intended to be generic, not CV32E40Pv1-specific.

Where should the templates go?

[DBees]

https://github.com/openhwgroup/programs/tree/master/process

contains a number of templates.