urcheon: make possible to add arbitrary version suffix

[illwieckz]

For example a nightly server can build map-parpax_2.7.1.dpk as map-parpax_2.7.1~nightly.dpk so the released map-parpax_2.7.1.dpk will take precedence, and reduce the risk of having a nightly build and a release build sharing the same file name despite having different checksum.

For example one can use the feature this way:

urcheon package --version-suffix='~nightly' src/map-parpax_src.dpkdir