prerelease variables to be defined before build

Description

Issue(s)

https://gitlab.e.foundation/e/backlog/-/issues/5231

Test procedures

example of build for star2lte

https://gitlab.e.foundation/e/priv/os/build/-/jobs/285221

Build with

DEVICES = any q device

FEATURE_BRANCH = v1-q-5231-version-semantic2

PRODUCT_PRERELEASE = beta

PRODUCT_PRERELEASE = 3

should result to a build with this kind of name

e-1.0-beta.3*

should be also visible once installing the build in settings / about phone / Android Version / /e/OS version

Screenshots

this one was no maintenance patch version, so only 0.23:

Check list

• Self review
• Test procedure explained
• Tested on fresh install
• Tested applied as an update