Add proto definition for boottime metrics

- Most of them are for migrating from existing historgram logging.
- Following three items added as those critical information were missing:
  SECONDARY_ZYGOTE_INIT_START, LAUNCHER_START, LAUNCHER_SHOWN

Bug: 132691841
Test: build only, follow-up CLs will be added later per each logging components

Change-Id: I26cbca3b6f2d9f990dde31ac0880272ac141ff36