[v9] Prepare docs for new version support policy

[lforst]

Description

This task involves preparing a docs PR to update the new version support policies

• Prepare docs for new Node version support ([v9] Bump minimum supported Node.js version #14257)
• Prepare docs for minimum ES2020 support (https://docs.sentry.io/platforms/javascript/troubleshooting/supported-browsers/ to raise minimum support to ES2020, new APIs in ES2020: https://caniuse.com/?search=es2020)
• Dropped framework versions