Dogfood: Update default disk encryption settings on macOS

[noahtalerman]

• @noahtalerman: During ADE, Fleet doesn't allow any FileVault deferrals.

Related user story

• Update default disk encryption settings on macOS #29250

[lukeheath]

Allen has completed several macOS setups the last couple of days and confirmed encryption was automatically enabled.

[fleet-release]

Encryption's bloom,
No FileVault deferrals now,
Safe harbor in clouds.