This PR adds new options to create_index operation:

• method: enum for setting different index types. Default: btree. Available options: btree, hash, gist, spgist, gin, brin.
• storage_parameters: optional storage parameters for the index.

Example operation to create a new hash index with custom fillfactor:

{
  "name": "10_create_index",
  "operations": [
    {
      "create_index": {
        "name": "idx_fruits_name",
        "table": "fruits",
        "columns": [
          "name"
        ],
	"method": "hash",
	"storage_parameters": "fillfactor = 70"
      }
    }
  ]
}

Furthermore, analyze now return the index method under the name method and the definition under definition.
Please note that the definition pgroll returns is not the SQL statement pgroll runs when running create_index migrations.

{
 "idx_fruits_name": {
   "name": "idx_fruits_name",
   "unique": false,
   "columns": [
     "name"
   ],
   "method": "hash",
   "definition": "CREATE INDEX idx_fruits_name ON public.fruits USING hash (name) WITH (fillfactor='70')"
 }
}

Closes #378