BigtableDataClient is missing sync methods

[ajaaym]

Add below sync method in BigtableDataClient.

• readRow
• readRows
• sampleRowKeys
• mutateRow
• bulkMutateRows
• checkAndMutateRow
• readModifyWriteRow

[igorbernstein2]

Currently each rpc has 2 entrypoints: callable and async. I don't think it makes sense to add sync variant for only readRow. So I think this should be expanded to include a sync variant for all RPCs

[ajaaym]

Agree. Should include sync variant of all RPCs.

[sduskis]

@elisheva-qlogic, can you please look at this one?

[igorbernstein2]

It should be pretty straight forward to add sync variants for all of the methods:
for readRow:

public Row readRow(String tableId, ByteString rowKey) {
  return ApiExceptions.callAndTranslateApiException(readRowAsync(tableId, rowKey));
}