Serializes FIELD-NAME, a field name from (gnu services configuration), to a snake case upper case string representation of the field name. Trailing ? in the name are dropped and - get replaced by _. When PREFIX is a string, it is prepended to the result.

For example the procedure would convert 'A-Field? to "A_FIELD".

Serializes CONFIG, a configuration from (gnu services configuration), and its FIELDS to a list of pairs. Each pair represents an environment variable. The first element of each pair is the variable name, the second is the value. When PREFIX is a string it is prepended to the variable name. If any of FIELDS' names are a member of EXCLUDED they won't be serialized. TRUE-VALUE and FALSE-VALUE will be used as a representation for respectfully #t and #f.