Support columns with duplicated names

[rekby]

1. Run local YDB https://github.com/ydb-platform/ydb/wiki/Local-run-postgres-tests

➤ echo "select 1 as a, 2 as a" | psql postgres://root:1234@localhost:5432/local

Error:

Status: GENERIC_ERROR
Issues:
<main>: Error: Type annotation, code: 1030
    <main>:1:1: Error: At function: RemovePrefixMembers, At function: PgSelect, At function: PgSetItem
        <main>:1:1: Error: Duplicated member: a

Expected behavior:

 a | a
---+---
 1 | 2
(1 row)

[rekby]

Additionally need support duplicated columns names in SDKs:
#3885