Create a unified get_parameters method for all multi-table synthesizers

[npatki]

Problem Description

The multi-table synthesizers allow users to set and get parameters. Setting parameters must be different for the different synthesizers -- as each has different options based on the underlying algorithm. However, getting the parameters should be more consistent.

Expected behavior

All synthesizers should have a single method called get_parameters() that returns all the parameters used for the synthesizer. It should include:

• Any parameters used during initialization (eg. locales, num_clusters, etc.)
• A nested dictionary called 'tables' with settings specific to each table. The format of the dictionary would vary based on the type of multi-table algorithm.

The expected behavior is for the public-facing synthesizer only (HMA). We'll file a separate issue for HSA, Independent and DayZ (enterprise features).

# HMASynthesizer
>>> hma_synth.get_parameters()
{
  'locales': ['en_US', 'fr_CA'], # add the init params as top level
  'verbose': True,
  'tables': { # the table specific params are now in a nested dictionary
    'users': {
      'table_synthesizer': 'GaussianCopulaSynthesizer', # only possible synthesizer for HMA
      'table_parameters': { # add the table-level parameters here
        'enforce_min_max_values': False,
        'default_distribution': 'truncnorm',
      }
    }
  }
}

Additional context

The get_table_parameters should also be updated to provide the given table's parameter entry:

>>> hma_synth.get_table_parameters('users')
{
    'table_synthesizer': 'GaussianCopulaSynthesizer', # only possible synthesizer for HMA
    'table_parameters': { # add the table-level parameters here
      'enforce_min_max_values': False,
      'default_distribution': 'truncnorm'
}