[ThemeGraphql] Getting values from StoreConfig is not possible

[vasilii-b]

Preconditions (*)

1. Magento 2.3-develop
2. Filled in fields for Html Head, Header and Footer sections under Content -> Design -> Configuration -> one selected row as per your wish
   

Steps to reproduce (*)

1. Open GraphiQL or any other tool to make queries to Magento store
2. Create a query to get some store configuration information (available from app/code/Magento/ThemeGraphQl/etc/schema.graphqls). The following is an example:

{
  storeConfig {
    head_shortcut_icon,
    default_title,
    title_prefix,
    title_suffix,
    default_description,
    default_keywords,
    head_includes,
    demonotice,
    header_logo_src,
    logo_width,
    logo_height,
    logo_alt,
    welcome,
    absolute_footer,
    copyright
  }
}

Expected result (*)

Returned values reflect values added in the admin area.

Actual result (*)

For requested fields, you've got nulls as response:

[naydav]

#318