enable adaptive encoding with an env var

[zachmu]

Added new CI configurations to exercise this code path.

Also added a compatibility-breaking changes to prevent older dolt clients from misinterpreting adaptive encoded values.

[coffeegoddd]

@zachmu DOLT

read_tests	from_latency	to_latency	percent_change
covering_index_scan	0.55	0.55	0.0
groupby_scan	9.91	9.91	0.0
index_join	1.86	1.86	0.0
index_join_scan	1.37	1.37	0.0
index_scan	22.28	22.69	1.84
oltp_point_select	0.27	0.27	0.0
oltp_read_only	5.28	5.28	0.0
select_random_points	0.54	0.54	0.0
select_random_ranges	0.56	0.55	-1.79
table_scan	22.28	22.69	1.84
types_table_scan	66.84	68.05	1.81

write_tests	from_latency	to_latency	percent_change
oltp_delete_insert	6.32	6.32	0.0
oltp_insert	3.13	3.13	0.0
oltp_read_write	11.45	11.45	0.0
oltp_update_index	3.19	3.19	0.0
oltp_update_non_index	3.13	3.13	0.0
oltp_write_only	6.09	6.09	0.0
types_delete_insert	6.91	6.91	0.0

[coffeegoddd]

@zachmu DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
e51012b	ok	5937471

version	total_tests
e51012b	5937471

correctness_percentage
100.0

[reltuk]

LGTM!

[coffeegoddd]

@zachmu DOLT

test_name	from_latency_p95	to_latency_p95	percent_change
tpcc-scale-factor-1	56.84	58.92	3.66

test_name	from_server_name	from_server_version	from_tps	to_server_name	to_server_version	to_tps	percent_change
tpcc-scale-factor-1	dolt	2662362	42.73	dolt	f445758	42.54	-0.44

[coffeegoddd]

@zachmu DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
7e4ff4b	ok	5937471

version	total_tests
7e4ff4b	5937471

correctness_percentage
100.0

[coffeegoddd]

@zachmu DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
f445758	ok	5937471

version	total_tests
f445758	5937471

correctness_percentage
100.0