chore: set schema and search_path

[usamoi]

• pgvecto.rs: chore: set schema and search_path #273
• pgvecto.rs-docs: docs for 'chore: set schema and search_path' pgvecto.rs-docs#19

closes #270

[cutecutecat]

Is the search_path global and would be shared by other extensions?

[cutecutecat]

It seems that this PR would fix pgvecto.rs target schema to vectors and require user to explicit set it.

Apart from this, I see there is a way of An extension might be relocatable during installation but not afterwards.
ref: https://www.postgresql.org/docs/16/extend-extensions.html#EXTEND-EXTENSIONS-RELOCATION

Could we set location at create script as:

SET LOCAL search_path TO @extschema@, public;

And use a pg function current_schema() to get it at regtypein and regoperatorin?
ref: https://www.postgresql.org/docs/16/functions-info.html#FUNCTIONS-INFO-SESSION

[usamoi]

Is the search_path global and would be shared by other extensions?

search_path can be local.

[usamoi]

use a pg function current_schema() to get it at regtypein and regoperatorin?

I think it's not how current_schema() works.

[cutecutecat]

This PR would lock pgvecto.rs operators installed at vectors schema.

Affect

CREATE EXTENSION vectors WITH SCHEMA xxx is forbidden from now.

Instead, user need to alter search_path=vectors to enable global access of operators and search_path=vectors, xxx to access other schema optional.

cc @VoVAllen