Add hooks to capture bootstrap durations in windows and linux (#2530)

These vars will be collected in CI-Metrics to help visualize **Wall Time
Component Breakdown**

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Co-authored-by: Florian Weikert <fwe@google.com>
Co-authored-by: Yun Peng <pcloudy@google.com>
Co-authored-by: Lily Gorsheneva <bgorshenev@google.com>