[feature] add dry run option

[boussaffawalid]

It would be very useful to add a dry run option that run all cpt steps except the actual package creation. This option can be used with Save created packages summary to get a summary of what will actually be build without building it

https://github.com/conan-io/conan-package-tools/tree/94af85cc7880f5205f0430a2164f0f59535f1e6b#save-created-packages-summary

[uilianries]

The default matrix is the combination of all possible compilers and OS. Is there any specific scenario that you need it? I can't see it as greatly useful.