The main `version` field in `package.json` will now include the beta
version (if present) rather than it being passed in via the CLI when
building. The `version` field is now a fully SemVer-compatible version,
with the added restriction that any prerelease portion of the version
must match the format `<build type>.<build version>`.
This brings the build in-line with the future release process we will
be using for the beta version. The plan is for each future release to
enter a "beta phase" where the version would get updated to reflect
that it's a beta, and we would increment this beta version over time as
we update the beta. The manifest gives us a place to store this beta
version. It was also important to replace the automatic minor bump
logic that was being used previously, because the version in beta might
not be a minor bump.
Additionally, the filename logic used for beta builds was updated to
be generic across all build types rather than beta-specific. This will
be useful for Flask builds in the future.
