Merge insert logics in row.rs & execute.rs into executor/insert.rs

[panarch]

…module

prior pr #1029

Insert execution code logics are splitted in data/row.rs and executor/execute.rs
By adding executor/insert.rs, it merges the codes into a single insert module.

[coveralls]

Pull Request Test Coverage Report for Build 3590936141

• 157 of 162 (96.91%) changed or added relevant lines in 4 files are covered.
• 7 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 98.594%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core/src/executor/execute.rs	2	3	66.67%
core/src/executor/insert.rs	149	153	97.39%

Files with Coverage Reduction	New Missed Lines	%
core/src/executor/aggregate/mod.rs	7	82.2%

Totals
Change from base Build 3590702792:	0.02%
Covered Lines:	36804
Relevant Lines:	37329

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💛 - Coveralls

[ever0de]

LGTM