Replace Groovy DSL doc-extension for asciidoctorj 3 compatibility

[mrotteveel]

Currently, we use asciidoctorj Groovy DSL for two extensions:

1. a preprocessor for PDF for the since/until rendering
2. a docinfo processor to add a canonical URL to the header of the HTML output

Unfortunately, asciidoctorj Groovy DSL is not compatible with asciidoctorj 3, and it doesn't look like it will get updated.

We need to replace them with "normal" asciidoctorj extensions. While doing so, we may want to consider replacing the since/until preprocessor with an inline macro instead of its current "abuse" of a style attribute.

[mrotteveel]

Given the docinfo processor is also used for the https://github.com/FirebirdSQL/firebird-documentation repository, we should consider creating this as a separate project so we can deploy to Maven Central and share between jaybird-manual and firebird-documentation