Allow location of configuration file to be specified
Currently, Assembler looks for a configuration file named antora-assembler.yml located in the same directory as the playbook. Like with the playbook file, it should be possible to pass the location of the configuration file either through the extension configuration or as a CLI option (likely using an AsciiDoc attribute). Not only does this allow the user to switch between different configurations, it also opens up the possibility of running the extension multiple times to run with different settings with a different set of component versions.
In the extension configuration, the key for the location of the configuration file should be config_file
. The default is ./antora-assembler.yml
. If specified using an AsciiDoc attribute, the attribute name should be antora-assembler-config-file
. For now, using the AsciiDoc attribute limits the use of the extension to a single configuration file. (If and when Antora supports CLI options per extension, that can be used instead).