Support different consolidation strategies in pull-package-versions

[BalassaMarton]

In case a central version already exists, the current implementation either discards the package version, or updates it in the central file only if --update is specified AND the referenced version is higher than the central version.
We should add options to fine tune this behavior. Some cases we should consider (reference refers to the Version in PackageReference and central to the Version in the existing PackageVersion, if any).

• Update only if reference > central
• Update only if reference > central and reference.major = central.major
• Skip if reference.major < central.major (and leave the warning or error to the CPVM implementation)

Also, multiple existing references with different versions should be consolidated using similar strategies.