Documentation toolchain enhancements

[barchetta]

For Helidon 4 we are planing to enhance the documentation toolchain. Here are some requirements:

High Priority:

• Search engine optimized (SEO) #981
• Table of Contents support

Medium Priority:

• Improved configuration metadata integration
• Local rendering ability

Low Priority:

• Tabbed widget. Generic and specialized for project creation (cli/maven/starter).
• URL compatibility with previous versions of docs