Add options clause to create table macro

[JCZuurmond]

resolves #147

Description

Adds an option clause macro which allows for adding options to a table via the config:

{{
  config(
    materialized='table',
    file_format='jdbc',
    options={
      'dbtable': 'my_table',
      'url': 'jdbc:sqlserver://${spark.serverName}:1433;databaseName=database;',
      'user': '${spark.adminUsername}',
      'password': '${spark.adminPassword}'
    }
  )
}}

Heavily inspired on #148. @friendofasquid : I went ahead, implemented a solution based on the examples you created, here to contribute back.

Checklist

• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt next" section.

[jtcohen6]

I'm all about it! Thanks @JCZuurmond, this looks great.

My only ask: Could you add options to the SparkConfig class here? That's where we track adapter-specific configs that can be set in dbt_project.yml, be recorded in manifest.json, and may or may not want custom validation.

[JCZuurmond]

Done!

[jtcohen6]

Thanks @JCZuurmond!