Add Codelist feature

Can pass directory to tool, this contains the code lists.

For any closed codelists, take codes from CSV files and put into ENUM's.

For current use see Eg. see https://github.com/openownership/data-standard/blob/master/schema/entity-statement.json#L64

Suggestion for use here:

If "openCodelist": true is on an object, don't do anything. If it's false or not there, we assume it's ok to carry on.

If "Codelist" property on an object, it should link to file.

• If file is a CSV. Load CSV and take off first row (headers). Take any non-empty values from first column and put as list on "enum" property of object.

Files can be:

• relative file names; in that case look relative to a directory that is passed as a new argument.

[jpmckinney]

FYI, OCDS Kit has a set-closed-codelists-enums command, which works whether the codelist is for a string field of an array field with string items, it works with +codelist.csv and -codelist.csv files, extensions, etc. https://ocdskit.readthedocs.io/en/latest/cli/schema.html#set-closed-codelist-enums