Support for INSERT .. RETURNING

[zachmu]

No description provided.

[github-actions]

	Main	PR
covering_index_scan_postgres	392.15/s	388.49/s	-1.0%
index_join_postgres	157.70/s	155.48/s	-1.5%
index_join_scan_postgres	188.23/s	188.27/s	0.0%
index_scan_postgres	12.66/s	12.58/s	-0.7%
oltp_point_select	2818.07/s	2862.47/s	+1.5%
oltp_read_only	1897.69/s	1906.97/s	+0.4%
select_random_points	113.14/s	113.42/s	+0.2%
select_random_ranges	135.18/s	136.06/s	+0.6%
table_scan_postgres	10.29/s	10.43/s	+1.3%
types_table_scan_postgres	5.41/s	5.42/s	+0.1%

[github-actions]

	Main	PR
Total	42090	42090
Successful	15732	15732
Failures	26358	26358
Partial Successes1	5190	5190

	Main	PR
Successful	37.3770%	37.3770%
Failures	62.6230%	62.6230%

Footnotes

1. These are tests that we're marking as Successful, however they do not match the expected output in some way. This is due to small differences, such as different wording on the error messages, or the column names being incorrect while the data itself is correct. ↩

[fulghum]

Code looks good once you get the tests passing.