Add ALTER TABLE ... ADD FIELD ...

[yaziine]

This is a sub-issue of #94 that focuses on adding a new field constraint.

We should be able to do the following:

genji> CREATE TABLE foo;
genji> INSERT INTO foo VALUES {name: "John Doe"};
genji> ALTER TABLE foo ADD FIELD age int;

If the field age already exists, we should return an error.

NOT NULL

The only constraint supported for now would be NOT NULL but a default value must be specified for the existing documents.

genji> ALTER TABLE foo ADD FIELD age int NOT NULL DEFAULT 50;
genji> SELECT * FROM foo;
{
  "name": "John Doe",
  "age": 50
}

Dot notation

We should also support the dot notation structure.
For example:

genji> ALTER TABLE foo ADD FIELD adress.zip int;
genji> INSERT INTO foo VALUES {name: "John Wick", age: 50, adress: {zip:75000}};
genji> SELECT * FROM foo;
{
  "name": "John Wick",
  "age": 50,
  "adress": {
    "zip": 75000
  }
}
genji> INSERT INTO foo VALUES {name: "John Wick", age: 50, adress: {zip:"Paris"}};
cannot convert "text" to "int64": type "text" incompatible with "integer"

The same goes for arrays:

genji> ALTER TABLE foo ADD FIELD animals.0 text;
genji> INSERT INTO foo VALUES {name: "John Lennon", age: 50, animals: ["bird"]};
genji> SELECT * FROM foo;
{
  "name": "John Lennon",
  "age": 50,
  "animals": [
    "cat",
  ]
}
genji> INSERT INTO foo VALUES {name: "John Lennon", age: 50, animals: [127]};
cannot convert "int8" to "string"