Filter blank lines from default_config

[nonk123]

Blank lines inside default_settings cause a cryptic parsing error along the lines of:

ERROR: Invalid config: Found invalid config 'kuma.default_settings': 

(Also note the wrong setting name; it's supposed to be default_settings without kuma.)

Example default_config which causes this:

      AUTOKUMA__DEFAULT_SETTINGS: |-
        http.notification_name_list: ["tg"]
        port.notification_name_list: ["tg"]
        group.notification_name_list: []
        
        http.expiry_notification: true
        http.max_redirects: 10
        
        *.interval: 20
        *.max_retries: 3