feat: refine APIs and docs

[tisonkun]

Verified with vector-rs:

https://vector.dev/docs/reference/configuration/sources/syslog/

sources:
  in:
    type: syslog
    address: 0.0.0.0:514
    mode: udp
    path: /path/to/socket

sinks:
  out:
    inputs:
      - "in"
    type: "console"
    encoding:
      codec: "text"

sources:
  in:
    type: syslog
    address: 0.0.0.0:601
    mode: tcp
    path: /path/to/socket

sinks:
  out:
    inputs:
      - "in"
    type: "console"
    encoding:
      codec: "text"