Migrate all attribute name/value pairs to Antora component descriptors

Starting in Antora 2.3, the component descriptors, e.g. antora.yml files, will support defining attribute key/value pairs much like the playbook.yml does. These attributes are global to the component itself and since Debezium only has a single component, this would work nicely. This essentially:

• Allows defining substitution key/value pairs along side the documentation, single repo.
• Allows defining attributes semi globally to avoid needing _attributes.adoc
• By not needing _attributes.adoc, works much more closely with downstream doc pipeline since we don't need to force include it.

In antora.yml, we'd essentially define things like:

asciidoc:
  attributes:
    prodname: 'Debezium'
    assemblies: '../assemblies'
    modules: '../../modules'
    mysql-connector-plugin-download: 'https://repo1.maven.org/maven2/io/debezium/debezium-connector-mysql/1.0.0.Final/debezium-connector-mysql-1.0.0.Final-plugin.tar.gz'
    mysql-version: '8.0'
    context: 'debezium'

Make sure to reference the current values maintained in playbook.yml when making this change. The awestruct image will need to be updated to Antora 2.3 when it becomes available.

See https://github.com/Naros/debezium/tree/DBZ-1687 and https://github.com/Naros/debezium.github.io/tree/DBZ-1687.
These were tested with a modified awestruct image using 2.3.0.alpha.2, worked perfectly!