Post-docsy migration tasks

[chalin]

Followup to:

• Migration to docsy theme #746

Site links:

• Docsy site is live in production https://www.jaegertracing.io
• Legacy site: https://legacy--jaegertracing.netlify.app

Hugo config & site pages:

• Simplify and consolidate - [CI] Consolidate Hugo config, drop obsolete packages and theme #1025
• Enable Hugo's default robots.txt
• Drop pre-docsy front matter that is no longer needed, such as hasParent, etc.
• .

Netlify:

• Remove docsy branch config - https://docsy--jaegertracing.netlify.app
• Setup legacy branch config - https://legacy--jaegertracing.netlify.app

Other:

• Upstream relevant local Docsy layout customization to Docsy repo
• Upgrade Docsy
• Trigger site reindexing by Google. Done via sitemap.xml section.
• Ensure legacy branch has robots meta set to noindex,nofollow
• Add @yurishkuro and Johan to the site's Google Search console member list as owners

Extra (nice to have, maybe later):

• Prepare for 🌆 Jaeger v1 End-of-life jaeger#6321 by, e.g., renaming config var from v2 to base, etc.
• Consider not fetching the blog posts data on every build?
• Switch to Hugo config dir rather than our custom WKSP feature