Update the reference guide hosted on GH pages

[manovotn]

The README file links to a reference guide hosted on GH pages - https://jakartaee.github.io/cdi-tck/
It seems this wasn't done for 4.1 which doesn't really matter now, but for 5.0 we should keep that in mind - hence this issue.

IIUIC, the way to do that is to update it in the contents of /docs, which then get published:

1. Build the reference guide
   1.1 mvn clean install -Drelease -DskipTests will do
2. Copy the generated HTML over the old one:
   2.1 cp doc/reference/target/generated-docs-html/cdi-tck-reference-guide.html docs/index.html
3. Commit and push to main, the pages should be served automatically.