RDB Shredder: switch to a HOCON config

[benjben]

Sister ticket to #250

RDB shredder and loader will be using the same config file.

Compression format from the config will have to be added to the SQS message.

Format:

{
  # Human-readable identificator, can be random
  "name": "Acme Redshift",
  # Machine-readable unique identificator, must be UUID
  "id": "123e4567-e89b-12d3-a456-426655440000",

  # Data Lake (S3) region
  "region": "us-east-1",
  # Shredder output compression, GZIP or NONE
  "compression": "GZIP",
  # SQS topic name used by Shredder and Loader to communicate
  "messageQueue": "messages",

  # Schema-specific format settings (recommended to leave all three groups empty and use TSV as default)
  "formats": {
    # Format used by default (TSV or JSON)
    "default": "TSV",
    # Schemas to be shredded as JSONs, corresponding JSONPath files must be present. Automigrations will be disabled
    "json": [ ],
    # Schemas to be shredded as TSVs, presence of the schema on Iglu Server is necessary. Automigartions enabled
    "tsv": [ ],
    # Schemas that won't be loaded
    "skip": [ ]
  },

  # Warehouse connection details
  "storage" = {
    # Database, redshift is the only acceptable option
    "type": "redshift",
    # Redshift hostname
    "host": "redshift.amazon.com",
    # Database name
    "database": "snowplow",
    # Database port
    "port": 5439,
    # AWS Role ARN allowing Redshift to load data from S3
    "roleArn": "arn:aws:iam::123456789012:role/RedshiftLoadRole",
    # DB schema name
    "schema": "atomic",
    # DB user with permissions to load data
    "username": "storage-loader",
    # DB password
    "password": "secret",
    # Custom JDBC configuration
    "jdbc": {"ssl": true},
    # MAXERROR, amount of acceptable loading errors
    "maxError": 10,
    "compRows": 100000
  },

  # Additional steps. analyze, vacuum and transit_load are valid values
  "steps": ["analyze"],

  # Observability and logging opitons
  "monitoring": {
    # Snowplow tracking (optional)
    "snowplow": null,
    # Sentry (optional)
    "sentry": null
  }
}

[chuwy]

The format here isn't final. It still misses buckets for stateless-discovery, which we'll implement in #263