Config: Support config by ENV. 支持用环境变量配置SRS。

[winlinvip]

参考Grafana: Override configuration with environment variables，所有配置都可以通过环境变量覆盖，这样非常适合云原生部署。

Do not use environment variables to add new configuration settings. Instead, use environmental variables to override existing options.

To override an option:

GF_<SectionName>_<KeyName>

Where the section name is the text within the brackets. Everything should be uppercase, . and - should be replaced by _. For example, if you have these configuration settings:

# default section
instance_name = ${HOSTNAME}

[security]
admin_user = admin

[auth.google]
client_secret = 0ldS3cretKey

[plugin.grafana-image-renderer]
rendering_ignore_https_errors = true

You can override them on Linux machines with:

export GF_DEFAULT_INSTANCE_NAME=my-instance
export GF_SECURITY_ADMIN_USER=owner
export GF_AUTH_GOOGLE_CLIENT_SECRET=newS3cretKey
export GF_PLUGIN_GRAFANA_IMAGE_RENDERER_RENDERING_IGNORE_HTTPS_ERRORS=true

[winlinvip]

Modifying and configuring environment variables is very useful, especially in K8s and Docker.

TRANS_BY_GPT3

[winlinvip]

Dup #2277