Add options to control Homebrew environment variable hints, analytics
notices, and new formulae/casks reports during system activation and
manual brew commands.
These follow the existing autoUpdate pattern: boolean options that
default to true (preserving current behavior) and set the corresponding
HOMEBREW_NO_* environment variable when disabled.
onActivation options affect brew bundle during darwin-rebuild switch.
global options affect interactive brew commands via environment.variables.
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