Allow to condition provides based on the version

[felipecrs]

          just need to omit it; it would be a potential upgrade to libpkgx if desired.

Originally posted by @jhheider in pkgxdev/pantry#5468 (comment)

Just to keep this tracked. openjdk 21+ provides bin/jwebserver while older versions does not.

It would be nice something like the following were allowed:

provides:
  - bin/java
  - program: bin/jwebserver
    if: {{version.major}} >= 21