Simplify join query in mosaic

[willeppy]

Can move the distinct on out potentially if used correctly
Current is:

`(SELECT ${asRelation(table)}.* EXCLUDE ${asColumn(
      joinKey
    )}, _joinTable.* FROM ${asColumn(
      table
    )} JOIN (${q2.toString()}) _joinTable ON ${asRelation(table)}.${asColumn(
      joinKey
    )} = _joinTable.${asColumn(joinKey)} ORDER BY ${asRelation(table)}.${asColumn(joinKey)})`

Can be updated to:

`(SELECT DISTINCT ON (${asRelation(table)}.${asColumn(joinKey)}) * FROM ${asRelation(table)} JOIN ${asRelation(rightTable)} ON ${asRelation(table)}.${asColumn(joinKey)} = ${asRelation(rightTable)}.${asColumn(joinKey)})`;

But need a flag for distinct on because this causes issues right now if table order switched

[willeppy]

Updated with new query format in willeppy/mosaic#5