Make casting from a timestamp without timezone to a timestamp with timezone configurable

[niebayes]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

In our time-series database project, we always interpret timestamps without a timezone as being in the UTC timezone. However, when we use the arrow cast function to convert a timestamp without a timezone to a specific timezone, the result isn't what we expect. This is because the cast function enforces an adjustment internally, which causes an unintended modification to the timestamp values during the cast process.

As specified in the doc and in the comment of codes, arrow cast will adjust the timestamp values if casting from a timestamp array without a timezone to a timestamp array with a timezone.

I propose to make such a behavior configurable and optional.

Describe the solution you'd like

A sound solution may be adding a boolean flag to CastOptions to make the arrow cast function not perform such an adjustment. This boolean flag may be named enable_timestamp_adjustment.

Describe alternatives you've considered

Additional context

#5827 stated that the behavior of the arrow cast function is somewhat confusing.

[tustvold]

Whilst perhaps not ideal, this behaviour can be achieved by first casting to a timestamp with a timezone of UTC and then casting to the desired target TZ.

That being said, if all timestamps are UTC, why not just store them as UTC timestamps? It isn't just the cast kernels that would need to be updated to support a non-spec-compliant interpretation of timestamps without a timezone.