sql: add an ability to disable CK constraints

Closes #4244

@TarantoolBot document
Title: an ability to disable CK constraints

Now it is possible to disable and enable ck constraints.
All ck constraints are enabled by default when Tarantool is
configured. Ck constraints checks are not performed during
standard recovery, but performed during force_recovery -
all conflicting tuples are skipped in case of ck_constraint
conflict.

To change CK constraint "is_enabled" state, call
-- in LUA
ck_obj:enable(new_state in {true, false})
-- in SQL
ALTER TABLE {TABLE_NAME} {EN, DIS}ABLE CHECK CONSTRAINT {CK_NAME};

Example:
box.space.T6.ck_constraint.ck_unnamed_T6_1:enable(false)
box.space.T6.ck_constraint.ck_unnamed_T6_1
- space_id: 512
  is_enabled: false
  name: ck_unnamed_T6_1
  expr: a < 10
box.space.T6:insert({11})
-- passed
box.execute("ALTER TABLE t6 ENABLE CHECK CONSTRAINT \"ck_unnamed_T6_1\"")
box.space.T6:insert({12})
- error: 'Check constraint failed ''ck_unnamed_T6_1'': a < 10'