feat scripts: jinja2 in sql

[danilshvalov]

SQL queries often have duplicate elements, such as fields in SELECT. I would like to put such elements in a separate file to reduce duplication.

This Pull Request adds the ability to use Jinja2 substitution in SQL queries. The following is an example of usage.

_fields.sql

id,
first_name,
last_name

select_user_by_id.sql

SELECT
{% include '_fields.sql' %}
FROM users
WHERE id = $1

select_users.sql

SELECT
{% include '_fields.sql' %}
FROM users
ORDER BY id

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