Custom type and property metadata during declaration

[gramian]

Currently one needs to use ALTER TYPE or ALTER PROPERTY to set a custom metadata key-value pair, ie:

CREATE DOCUMENT TYPE doc;
ALTER TYPE doc CUSTOM coolness = 1;

CREATE PROPERTY doc.num INTEGER (readonly true);
ALTER PROPERTY doc.num CUSTOM oflines = 2;

It would be more convenient to directly set metadata in CREATE x TYPE or CREATE PROPERTY. As for ALTER, the syntax introducing the metadata pairs can also be introduced with the CUSTOM keyword, like:

CREATE DOCUMENT TYPE doc CUSTOM coolness = 10;

CREATE PROPERTY doc.num INTEGER (readonly true) CUSTOM oflines = 1;

Furthermore, multiple custom key-value pairs should be passable separated by commas, like for attributes:

CREATE VERTEX TYPE vex CUSTOM x = 'width', y = 'height';

I will look into the SQL definition if this is not too hard and report in this thread, which can also be moved to an issue.