Extend `@module` annotation for `external` to allow import assertions

[Kingdutch]

As of version 17, Node.js requires import assertions (according to the import assertions proposal) when you want to import non-JS files (such as JSON).

In ReScript we can currently make an import statement for a JSON module using @val @module("mdn-data/css/types.json") external types : types = "default" but this will cause a type error: TypeError [ERR_IMPORT_ASSERTION_TYPE_MISSING]: Module "file:///mdn-data/css/types.json" needs an import assertion of type "json"

The generated import statement is import TypesJson from "mdn-data/css/types.json"; but the correct format would be import TypesJson from "mdn-data/css/types.json" assert { type: "json" };. There's currently no way that I'm aware of to make this happen.

My proposal is to add a second optional argument to @module() that contains the assertion object. Please note that the specification chose for an object over a string on purpose because other assertions may be added in the future. So we should follow their example (i.e. rather than allowing only the string "json").