feat: generate metadata from the plan

Summary

• feat: generate metadata from the plan

Previously, we returned metadata from tarantool, not from the plan. Sometimes it led to disinformation, for example (pay attention to the types):

picodata> select 1 from g
---
- metadata:
  - {'name': 'COL_1', 'type': 'integer'}
  rows: []
...

picodata> explain select 1 from g
---
- - projection (1::unsigned -> "COL_1")
  - '    scan "G"'
  - 'execution options:'
  - sql_vdbe_max_steps = 45000
  - vtable_max_rows = 5000
...

---

• Close #...
• Cherry-pick to: none / 24.2 / 24.3
• Docs follow-up: not necessary / new issue