Support non-public schema for PostgreSQL 15+

[lewijw]

Description

For PostgreSQL setup, the doc says:

-- PostgreSQL 15 requires additional privileges:
GRANT ALL ON SCHEMA public TO airflow_user;

For security-concerned customers that do not want to use the public schema, it would be nice if the schema to use could be configurable.

Use case/motivation

For security sake, use a schema other than public.

Related issues

No response

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct