build: Select stage/prod env based on $(VERSION)

[camscale]

Select the appropriate stage or prod GitHub Actions environment when running tag-build or tag-publish based on $(VERSION). If a version string has no pre-release suffix, or it has -cloud. then it is considered a prod release and will be built/published in the build-prod/publish-prod environment. Other pre-release tags will be built/published in the build-stage/publish-stage environment.

This can be overridden by specifying the environment name when building or publishing:

make ENVIRONMENT=build-prod tag-build
make ENVIRONMENT=publish-prod tag-publish

[fheinecke]

This needs an e ref update and to be merged in sync with https://github.com/gravitational/teleport.e/pull/4122