Add SEO <meta> keywords

[davsclaus]

Apache Kafka has on their front page

We should have keywords too for Apache Camel

[davsclaus]

@zregvart wonder if you can help with this

[zregvart]

We have support for this but we lack the content. For each Hugo built, that is *.md files in content directory keywords front matter needs to be added similar how description is done. Similarly for Antora built content keywords Asciidoc attribute needs to be set in *.adoc files.