Rework Upgrade Report support

[fabapp2]

What needs to be done

The Upgrade Report creation should be simplified.
It basically consists of a template and some logic that finds matches and provides them to the template and the condition which defines if the section should be rendered. The condition is in most cases true if matches were found.

Why it needs to be done

The Spring Boot upgrade report requires multiple classes and defining the sections in Asciidoctor syntax through a fluent API. this is cumbersome and time-consuming.

Implementation

The template for each section should be provided in the recipe YAML.
One class per section should be defined which is data provider and condition.

[fabapp2]

The report creation with AsciidoctorJ fails when the default charset is set to US-ASCII (as set by the JDK I used) and the error complains about incompatible encodings of UTF-8 and US-ASCII. The cause seems to be RubyString which uses the default encoding and fails if the template encoding is not the same.
jruby/jruby#6588
asciidoctor/asciidoctorj#815

The problem is solved when either the file is encoded using US-ASII (no option)
Or setting export JAVA_TOOL_OPTIONS=-Dfile.encoding="UTF-8"

• Add precondition check and inform users when Charset.defaultCharset() is not UTF-8