ORCA currently exists as a standalone repo. However, it requires
significant coordination to build GPDB with ORCA or make changes to
ORCA. With these commits, we get rid of the versioning concept, which
hopefully will make both building and developing on ORCA much easier
(and you won't hit version mismatch issues anymore)

The GPDB build process will now also build ORCA using make. If you want
to run the ORCA unit tests, those will continue to use cmake/ctest.
Cmake will not install ORCA or build ORCA with GPDB, it is only used to
run ORCA unit tests.

This merge commit includes all ORCA commits from when ORCA was
open-sourced until f6044123 (v3.97.1)

This commit was generated using `git subtree add -P src/backend/gporca
git@github.com:greenplum-db/gporca.git HEAD`.

Add 'src/backend/gporca/' from commit 'f6044123'
git-subtree-dir: src/backend/gporca
git-subtree-mainline: b6fbabdb
git-subtree-split: f6044123

Discussion: https://groups.google.com/a/greenplum.org/d/msg/gpdb-dev/q4g73r6Y_qA/OpZXDFFwAwAJ