]MultiProgress API is not usable in real world scenarios

[dawidpilarski]

Because everything in MultiProgress Bar is templated it makes it not usable in cases, where amount of progress bars is not known at compile-time and this is a common case.

for example:

• imagine cp program, that prints the progress. Amount of files is not known at compile time
• article of bfilipek: https://www.bfilipek.com/2020/02/inidicators.html (where you are the author) shows docker progress bars. A number of those bars is not known at compile time.