Re: Conflict Detection and Resolution

The patches have been rebased on the latest pgHead following the merge
of the conflict detection patch [1]. The detect_conflict option has
been removed, and conflict detection is now enabled by default. This
change required the following updates in resolver patches:
patch-0001:
- Removed dependency on the detect_conflict option. Now, default
conflict resolvers are set on CREATE SUBSCRIPTION if no values are
provided.
- To keep the behavior unchanged, the default resolvers are now set as -
insert_exists = error
update_exists = error
update_differ = apply_remote
update_missing = skip
delete_missing = skip
delete_differ = apply_remote
- Added documentation for conflict resolvers.

patch-0002:
- Removed dependency on the detect_conflict option.
- Updated test cases in 034_conflict_resolver.pl to reflect new
default resolvers and the removal of the detect_conflict option.

patch-0003:
- Implemented resolver for the update_exists conflict type. Supported
resolvers are: apply_remote, keep_local, error.

*The timestamp-based resolution patch is not yet rebased due to its
dependency on the detect_conflict option for handling two-phase and
parallel apply-worker workflows. The behavior needs to be reassessed.

To Do:
patch-0001: Add support for pgdump.
patch-0002 and 0003:
- Optimize by avoiding the pre-scan for conflicts in insert_exists
and update_exists when the resolver favors error or skips applying
remote changes.
- Improve the current recursive method used for multiple key conflict
resolution in update_exists.

Thanks Ajin for working on the docs.

[1] - https://www.postgresql.org/message-id/CAA4eK1%2BKb4i64cRD7MCUGkABNzBgQkP8vr5t01N%2BL_8GtwPgcA%40mail.gmail.com

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Thanks,
Nisha