Improve handling of multiple parallel errors during commit

Referencing internal discussion on https://couchbase.slack.com/archives/G0186DG1YT0/p1624379150010500.

All errors that happen during commit are returned in the final error message.  This has no functional impact on the transaction itself but can involve returning a large amount of data that must be parsed.

Some possible solutions are discussed on the link.  A balance needs to be struck to return an appropriate and useful amount of diagnostic detail.

This work will want to be done as part of CBD-3703.