add support for custom --log-config

[regisin]

Uvicorn let's you specify a custom format for logging: https://uvicorn.dev/settings/#logging

This PR allows the user to do so via fastapi-cli: fastapi dev --log-config /path/to/log_config.yaml.

Example config file (includes client IP in the logs):

version: 1
disable_existing_loggers: false

formatters:
  default:
    "()": uvicorn.logging.DefaultFormatter
    fmt: "%(levelprefix)s %(asctime)s | %(message)s"
    use_colors: true
  access:
    "()": uvicorn.logging.AccessFormatter
    "fmt": '%(levelprefix)s %(asctime)s | %(client_addr)s - "%(request_line)s" %(status_code)s'
    use_colors: true

handlers:
  console:
    class: logging.StreamHandler
    formatter: default
    stream: ext://sys.stdout
  access:
    class: logging.StreamHandler
    formatter: access
    stream: ext://sys.stdout

root:
  level: INFO
  handlers: [console]

loggers:
  uvicorn.error:
    level: INFO

  uvicorn.access:
    level: INFO
    propagate: false
    handlers: [access]

[svlandeg]

Hi, thanks for the PR!

This seems to be a duplicate of #36 though, which also has tests. So I'll go ahead and close this one for now.

[regisin]

Oh yes, that looks much better, thanks for checking.