feat(postgres): implements `ltree`

[gazorby]

Hasura's implementation:

• https://hasura.io/blog/query-hierarchical-data-structures-on-hasura-with-postgres-ltree
• https://hasura.io/docs/2.0/queries/postgres/filters/ltree-operators/

Feature Request Type

• Core functionality
• Alteration (enhancement/optimization) of existing feature(s)
• New behavior

Description