use cookicutter + "template" branch to UX in creation and upgrades

[yarikoptic]

• templating: instead of "Replace hello_cmd with the ..." etc, make this project into https://github.com/cookiecutter/cookiecutter template. Users then should be able to just enter the name and all the fields would be filled in
• upgrades: Analogous how datalad-crawler establishes incoming branch different from master, and how we established "3rd" branch in other projects for "vanilla" 3rd party code, and reflecting on such recommended practice in https://github.com/cookiecutter/cookiecutter/issues/784#issuecomment-839074042
  • in this repo use cookiecutter branch
  • adjust README.md to say that actual extension project should checkout master main (or whatever they want) from that cookiecutter branch to introduce any changes beyond cookiecutter config etc. Then for upgrades - checkout cookiecutter, re-cut, and merge into main.

there is also https://cruft.github.io/cruft/ which might be doing both of the above. Yet to check it out to see if worth using it instead of tandem above.

[ypid-work]

Checkout Copier before deciding how to rework this template. https://copier.readthedocs.io/en/stable/comparisons/

I am using Copier for a few years already and can recommend it. But I must say I have no experience with cookicutter so I don’t know how cookicutter developed.