Add config to collect statistics, enable in TPC-H benchmark

[Dandandan]

Which issue does this PR close?

Closes #797

Allows configuring the CollectLeft threshold in Ballista and enable collecting statistics in TPC-H benchmark.

(2,5,7,8,9,10,11,14,15,16,21 are faster with statistics available because of better join selection)

	without collecting stats	with collecting stats
1	1450.91	1451.59
2	1462.58	846.69
3	1146.47	1142.10
4	935.40	936.54
5	1767.56	1357.01
6	516.96	518.90
7	2114.79	1667.12
8	2503.08	1707.93
9	2175.66	1734.37
10	1403.69	1158.69
11	1115.91	765.67
12	1080.43	1080.57
13	1244.99	1243.37
14	938.96	519.41
15	1683.18	1511.17
16	1336.33	1151.75
17	1963.21	1963.03
18	2001.95	2002.84
19	1294.52	1259.65
20	1250.44	1248.19
21	1771.44	1555.07

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?