Migrate to Antora Documentation

* Use `providers.provider` for `modifiedFiles`.
This defers the looking up of `modifiedFiles` until it is used. It
also allows other tasks to be ran from the non-primary work tree.
Working in another work tree is essential for Antora which will clone
each branch/tag into a new work tree to process it.

* Migrate Structure

* Insert explicit ids for headers

* Fix image::image

* Copy default antora files

* Fix indentation for all pages

* Split files

* Generate a default navigation

* Remove includes

* Fix cross references

* Enable Section Summary TOC for small pages

* Polish nav.adoc

* Fix duplicate ids

* Escape {firstname} and {lastname}

* Remove links to htmlsingle and pdf Formats

* Fix broken links

* Disable attributes for ${debezium-version}

* Migrate to Asciidoctor Tabs

* Move to src/reference/antora

* Remove Asciidoctor Build

* deploy-docs only spring-projects

CONTRIBUTING.adoc

@@ -96,10 +96,10 @@ To build api Javadoc (results will be in `build/api`):
 ./gradlew api
 ----
 
-To build the reference documentation (results will be in `build/docs/asciidoc` and `build/docs/asciidocPdf`):
+To build the reference documentation (results will be in `build/site`):
 
 ----
-./gradlew reference
+./gradlew antora
 ----
 
 To build complete distribution including `-dist`, `-docs`, and `-schema` zip files (results will be in `build/distributions`):