Store boot events as raw data instead of parsing it

This CL stores the host stat events in a raw format so parsing can
be done in userland where it's more flexible to do changes.

Tested:
```
busctl call --verbose com.google.gbmc.boot_time_monitor \
  /xyz/openbmc_project/time/boot/host0 \
  xyz.openbmc_project.Time.Boot.Checkpoint GetCheckpointList

MESSAGE "a(sxx)" {
        ARRAY "(sxx)" {
                STRUCT "sxx" {
                        STRING "Shutdown:BEGIN";
                        INT64 1721722017000;
                        INT64 569778660;
                };
                STRUCT "sxx" {
                        STRING "Shutdown";
                        INT64 1721722028000;
                        INT64 569789660;
                };
                STRUCT "sxx" {
                        STRING "HostState:Off";
                        INT64 1721722411715;
                        INT64 569868660;
                };
                STRUCT "sxx" {
                        STRING "OSStatus:Inactive";
                        INT64 1721722411759;
                        INT64 569868710;
                };
                STRUCT "sxx" {
                        STRING "HostState:Off";
                        INT64 1721722511519;
                        INT64 82500;
                };
                STRUCT "sxx" {
                        STRING "OSStatus:Inactive";
                        INT64 1721722511536;
                        INT64 82510;
                };
                STRUCT "sxx" {
                        STRING "HostState:Running";
                        INT64 1721722596037;
                        INT64 167010;
                };
                STRUCT "sxx" {
                        STRING "OSStatus:Standby";
                        INT64 1721722718742;
                        INT64 289720;
                };
                STRUCT "sxx" {
                        STRING "Loader";
                        INT64 136000;
                        INT64 430620;
                };
                STRUCT "sxx" {
                        STRING "Userspace:BEGIN";
                        INT64 1721723134000;
                        INT64 567380;
                };
                STRUCT "sxx" {
                        STRING "Userspace";
                        INT64 1721723167000;
                        INT64 600380;
                };
        };
};

```

Google-Bug-Id: 296787899
Change-Id: I359dd43da7c302151d2b6c226809de424f8967d2
Signed-off-by: Medicine Yeh <medicineyeh@google.com>
6 files changed