good first issue
説明
Creating a grouing query string (e.g. all( group(customer) each(output(sum(price))) ) ) can be difficult with multi-level grouping, having a UI to construct the string a la the querybuilder might help.
Can be useful as a validator, too - paste a string into a field, and auto-generate an pretty-printed view
hence both ways from structured to string and vice versa
see #16870 for implementation suggestion