mozanalysis's `DataSource` should wrap metric-config-parser's `DataSource` instead of almost duplicating the functionality

[danielkberry]

As discussed here, mozanalysis's DataSource object contains an almost identical set of parameters as metric-config-parser's DataSource. This leads to the need for converter methods (example) and unnecessary confusion over objects. I propose replacing mozanalysis's DataSource object with something like:

from metric_config_parser import DataSource
from mozanalysis.types import AnalysisUnit

class ExperimentDataSource:
  data_source: DataSource
  app_id: str
  analysis_unit: AnalysisUnit

  def build_query(self, ...) -> str:
     ...