feat(semantic-release): don't build changelog on prerelease branches
By default, semantic-release build changelog even for prerelease
branches which looks like duplicated entries to users.
Use a workaround to avoid changelog generation for prerelease branches
by building the configuration in several steps instead of a direct
module.exports at the top.
There are no effect on this project since the branches configuration
attribute only contains stable but can be used for other project
with the only change to declare prerelease branches.
release.config.js: rework the configuration file to conditionnally
execute @semantic-release/changelog and add its assets to the git
plugin.