Add `compute=False` option to `to_snowflake`

[jrbourbeau]

Users sometimes want finer control over exactly when this compute is triggered. This matches what we do in other to_* methods like to_csv, to_parquet, etc.

[jrbourbeau]

Will plan to merge in a bit if no further responses. This should be a pretty uncontroversial change.

[dchudz]

@jrbourbeau maybe go ahead and merge now?

[jrbourbeau]

Thanks for the reminder. Forgot to circle back to this one