dreport: Add phosphor-fan-monitor data to dump

Send the USR1 signal to phosphor-fan-monitor to collect its dump data as
part of a BMC dump.

Tested:

~/BMCDUMP.139F210.00000041.20220908143628_out/archive$ cat fan_monitor_dump.json
{
    "logs": [],
    "sensors": {
        "sensors": {
            "/xyz/openbmc_project/sensors/fan_tach/fan0_0": {
                "functional": true,
                "in_range": true,
                "present": true,
                "prev_tachs": "[11904,11867,11904,11904,11867,11904,11867,11904]",
                "prev_targets": "[18000,0,0,0,0,0,0,0]",
                "tach": 11904.0,
                "target": 18000,
                "ticks": 0
            },
     ...
}

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I1173a38a755edff14ee0d418ec29ac0c583a790f