Feature request: impl AppenderParams for tuples up to certain arity

[rben01]

Passing data to Appender::append_rows is not as easy as it could be. If your data is heterogenous, then you cannot put it in an array. But using params![] correctly can be tricky due to lifetime issues caused by the references. For instance, you can't call appender.append_rows(iterator.map(|(foo, bar)| params![foo, bar])) because foo and bar are owned by the closure and therefore will not live as long as the references created by params. If foo and bar are themselves references, then you can manually write out [foo as &dyn ToSql, bar as &dyn toSql], but this is inconvenient compared to params!.

Ideally, AppenderParams would be implemented for tuples of ToSql up to some arity. This would allow users to easily pass heterogenous data to an Appender.