Add primary key config to tableInfo

[asdine]

This PR fixes how the pk() function works with __genji_tables.
It adds information about the primary key of that table, so that pk can pick it up correctly.

Before:

genji> create table foo;
genji> create table bar(a integer);
genji> SELECT pk(), * from __genji_tables;
json: error calling MarshalJSON for type document.jsonDocument: cannot decode buffer to uint64

After:

genji> create table foo;
genji> create table bar(a integer);
genji> SELECT pk(), * from __genji_tables;
{
  "pk()": "bar",
  "table_name": "bar",
  "store_id": "dF9LVloqBA==",
  "field_constraints": [
    {
      "path": [
        "a"
      ],
      "type": 16,
      "is_primary_key": false,
      "is_not_null": false
    }
  ],
  "read_only": false
}
{
  "pk()": "foo",
  "table_name": "foo",
  "store_id": "dF9LVlljTQ==",
  "field_constraints": [],
  "read_only": false
}