syntax: this version of e2factory introduces a new syntax version

syntax: this version of e2factory introduces a new syntax version
with the following features:
 * env attribute in source configuration
 * env attribute in result configuration

Support for old configuration versions is discontinued as versions
2.3.4 or above handle result specific environment in a stricter way,
leading to issues when environment for non-existent results is
configured.

Signed-off-by: Gordon Hecker <gh@emlix.com>