Workflow and tools for switching picongpu versions

[pordyna]

Our documentation doesn't describe a workflow on how to switch to a new commit (version) and reuse a simulation setup created with a different version.
There are several things that can go wrong in such a process, e.g., a user should know that they are supossed to remove the .build directory before recompiling. They also need to update files that are copied to the example directory (when using pic-create), such as the .tpl templates. Making changes to .cfg and .param files is sth a user may think about since they are already editing those, but, I think, updating, e.g., .tpl files may be not that obvious. The default tbg template is a relative path in the setup directory, so not updating it may lead to users running into problems that were already fixed in the repository (Just like it recently happened to @HighIander).

@BrianMarre suggested adding a new command line tool for updating setups, we could probably reuse pic-create for that.
This issue is a result of an offline discussion with @psychocoderHPC @sbastrakov @BrianMarre and @steindev.

I hope, I didn't miss anything important in this summary. If so, please comment down below.

[wmles]

This would be a really useful tool if it works! In my experience, it's always easier to start with a working example in the new version and edit this to incorporate the old changes.
But I fear it's far from trivial to write such a tool, it would have to track the changes in the signatures of the .param files. This is possible to do once between major versions but would require a lot of work/discipline to maintain that in the dev branch!

[sbastrakov]

Oh i think the idea for the tool was not to automatically account for changes in .param files with PIConGPU version, that would be on a user anyways. But at least to keep the rest intact, so that e.g. after the update tbg -t etc/picongpu/hemera-hzdr/fwkt_v100.tpl ... would use the updated .tpl file version and not potentially old one in user's input directory.