feat(psql): introduce column type `ltree` #1924

Job	Run time
Build `sea-query-binder` (async-std, rustls)	3m 15s
Build `sea-query`	1m 17s
Clippy	3m 59s
Build `sea-query-postgres`	1m 13s
Build `sea-query-rusqlite`	51s
Rustfmt	20s
Derive Tests	56s
Unit Test	2m 48s
MariaDB (10.6, sqlx_mysql)	2m 14s
MySQL (8, sqlx_mysql)	1m 45s
MySQL (5.7, sqlx_mysql)	2m 16s
PostgreSQL (14.4, postgres)	1m 9s
PostgreSQL (14.4, sqlx_postgres)	2m 10s
PostgreSQL (13.7, postgres)	1m 14s
PostgreSQL (13.7, sqlx_postgres)	1m 41s
PostgreSQL (12.11, postgres)	1m 8s
PostgreSQL (12.11, sqlx_postgres)	1m 45s
Any	1m 47s
SQLite (rusqlite)	27s
SQLite (sqlx_sqlite)	1m 12s
	33m 27s

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