Document CLI telemetry and auto-upgrade

[mintlify]

Summary

• Added a new Telemetry section to the CLI installation page documenting the --telemetry flag and environment variables (MINTLIFY_TELEMETRY_DISABLED, DO_NOT_TRACK) for opting out of anonymous CLI usage telemetry.
• Removed the deprecated mint upgrade command section from the CLI page, since configuration upgrades from mint.json to docs.json now happen automatically when running mint dev, mint broken-links, or mint rename.
• Updated the "Upgrading from mint.json" instructions on the Global settings page to reflect the new auto-upgrade behavior.

What shipped

The CLI now collects anonymous usage telemetry (enabled by default, easily disabled) and automatically upgrades legacy mint.json files to docs.json — the standalone mint upgrade command has been removed.

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Note

Low Risk
Low risk documentation-only change updating CLI usage guidance; no runtime or configuration logic is modified in this PR.

Overview
Updates CLI docs to replace the deprecated mint upgrade guidance with the current mint version section and a new Telemetry section explaining opt-out via --telemetry and env vars (MINTLIFY_TELEMETRY_DISABLED, DO_NOT_TRACK).

Revises the mint.json migration instructions to reflect automatic upgrade to docs.json triggered by running commands like mint dev (and related CLI commands), instead of a dedicated upgrade command.

^{Written by Cursor Bugbot for commit 998681b. This will update automatically on new commits. Configure here.}

[mintlify]

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[ethanpalm]

Closing as duplicate — the telemetry content is covered by #5039 and the auto-upgrade content is covered by #5049. Both of those PRs will be reviewed separately.