update image to 3.0.0-beta.2; add 3.0 to docsearch config
- update image to Antora 3.0.0-beta.2
- add 3.0 to docsearch config and remove 2.1 and 2.2
- remove global-table-attributes-tree-processor.js extension
- remove xref validator and replace with Antora's log level and format