Add support for primary key constraints in create_table operation

[kvch]

This PR adds support for setting primary key constraints in the constraints option of create_table.

Please note that if you set primary keys in columns, you are not allowed to configure primary_key constraints.

This configuration method is superior to marking columns as primary keys in the list columns, because it supports indexing options and deferring constraint checks.

Allowed options:

• columns (required)
• index_parameters.tablespace
• index_parameters.storage_parameters
• index_parameters.include_columns
• deferrable
• initially_deferred

Example:

{
  "name": "50_create_table_with_table_constraint",
  "operations": [
    {
      "create_table": {
        "name": "phonebook",
        "columns": [
          {
            "name": "id",
            "type": "serial",
          },
          {
            "name": "name",
            "type": "varchar(255)"
          }
        ],
        "constraints": [
          {
            "name": "my_pk",
            "type": "primary_key",
            "columns": [
              "id"
            ] 
          }
        ]
      }
    }
  ]
}

[andrew-farries]

This looks nice 👍

Can we also add an example migration that shows how to create PKs using a table constraint?