fix indentation in dcos

[Kowalskiexe]

Fix indentation in example in docs

Currently:

 pgsql:
    db_conn:
      host: "localhost"
      port: "5432"
      user: "usr_replica"
      password: "never_commit_passwords"
      database: "db_replica"
      charset: 'utf8'
      connect_timeout: 10
      schema_mappings:
        loxodonta_africana: elephas_maximus
      limit_tables:
        - loxodonta_africana.foo
      skip_tables:
        - loxodonta_africana.bar
      copy_max_memory: "300M"
      grant_select_to:
        - usr_readonly
      lock_timeout: "10s"
      my_server_id: 100
      replica_batch_size: 3000
      replay_max_rows: 10000
      sleep_loop: 5
      batch_retention: '1 day'
      copy_mode: 'file'
      out_dir: /tmp

Should be:

pgsql:
  db_conn:
    host: "localhost"
    port: "5432"
    user: "usr_replica"
    password: "never_commit_passwords"
    database: "db_replica"
    charset: 'utf8'
    connect_timeout: 10
  schema_mappings:
    loxodonta_africana: elephas_maximus
  limit_tables:
    - loxodonta_africana.foo
  skip_tables:
    - loxodonta_africana.bar
  copy_max_memory: "300M"
  grant_select_to:
    - usr_readonly
  lock_timeout: "10s"
  my_server_id: 100
  replica_batch_size: 3000
  replay_max_rows: 10000
  sleep_loop: 5
  batch_retention: '1 day'
  copy_mode: 'file'
  out_dir: /tmp
  type: pgsql

https://pg-chameleon.readthedocs.io/en/main/configuration_file.html#postgresql-source-type-experimental