Adding the possibility to scale the atom distribution for the synthetic atom distributions in the benchmark

[Iximiel]

Description

Please, don't ask me to backport this to 2.10, it would be a mess 🙏

• I added another decorator to the atom distribution collections that scales the given atomic distribution.
• I updated the test for this (also with a decorator that decorates: it is tagged as sphere-reply212) and I made the replicate test more robust.
• I removed the memory cost from the decorator that replicates the trajectory by making a small change in the API, that i mitigated by setting up a small override in the base class of AtomDistribution, so there is no impact in the rest of plumed, apart in two tests (fixed with a minor change)
• I implemented the new "scale" decorator as an option for the benchmark tool
• I updated the changelog also with older changes

Now I am tempted to add also a "wiggle" decorator, but it will be matter of another PR

Target release

I would like my code to appear in release v2.11

Type of contribution

• changes to code or doc authored by PLUMED developers, or additions of code in the core or within the default modules
• changes to a module not authored by you
• new module contribution or edit of a module authored by you

Copyright

• I agree to transfer the copyright of the code I have written to the PLUMED developers or to the author of the code I am modifying.

• the module I added or modified contains a COPYRIGHT file with the correct license information. Code should be released under an open source license. I also used the command cd src && ./header.sh mymodulename in order to make sure the headers of the module are correct.

Tests

• I added a new regtest or modified an existing regtest to validate my changes.
• I verified that all regtests are passed successfully on GitHub Actions.