chore(release): prepare release 1.20.0 - #11152

This PR prepares the release 1.20.0.

Summary by cubic

Description

Prepares the axios v1.20.0 release by bumping all version references so package metadata and the runtime export stay in sync. Consumers will now see VERSION report 1.20.0 instead of 1.19.0.

• Updates package.json and package-lock.json from 1.19.0 to 1.20.0.
• Updates lib/env/data.js to export VERSION "1.20.0".
• No functional changes; only the reported/versioned metadata changes.

Docs, testing, and semver

• Docs: Update /docs/ to reference 1.20.0 in install snippets and release notes.
• Testing: No tests modified; none required for a metadata-only version bump.
• Semantic version impact: Minor release (1.20.0). No breaking changes in this PR.

^{Written for commit 7f96e5e. Summary will update on new commits.}