API: Support server/pid/service label for exporter and api.

[chundonglinlin]

1.Use Prometheus Exporter, a server, pid and service label will be added to srs_build_info, for example:

# HELP srs_build_info A metric with a constant '1' value labeled by build_date, version from which SRS was built.
# TYPE srs_build_info gauge
srs_build_info{server="vid-90759d6",service="28d8h44y49",pid="19957",build_date="2023-01-17 07:33:00",major="5",version="5.0.134",code="Bee",label="cn-beijing",tag="cn-edge"} 1

2.Each API response, should return pid and service, for example, http://localhost:1985/api/v1/versions:

{
    "code": 0, 
    "server": "vid-90759d6", 
    "service": "28d8h44y49", 
    "pid": "19957", 
    "data": {
        "major": 5, 
        "minor": 0, 
        "revision": 134, 
        "version": "5.0.134"
    }
}