Add global and per feed configuration(integrate feeds download)

[davidgamez]

Describe the problem

As part of #1301, we needed to add global and per-feed configurations to allow more flexibility in the feeds' processing.

Proposed solution

Tasks:

• Design SQL entities to model global configuration keys and per-feed configuration.
• Create a "configuration service" exposing a get_key Python function.
• Using the newly created configuration service, update the feed download process to add additional HTTP headers per specific feeds.

Alternatives you've considered

No response

Additional context

No response

[davidgamez]

I had a quick session with ChatGPT few months ago an this was the resulting schema. Please take it as a starting idea, be free to change it as needed.

-- 1. Catalog of allowed keys + optional global values
CREATE TABLE config_key (
  namespace     text        NOT NULL,              -- e.g. 'reverse_geolocation'
  key           text        NOT NULL,              -- e.g. 'country_fallback'
  description   text,
  default_value jsonb,                             -- fallback if nothing else
  updated_at    timestamptz NOT NULL DEFAULT now(),
  PRIMARY KEY (namespace, key)
);

-- 2. Per-feed overrides
CREATE TABLE config_value_feed (
  feed_id       varchar(255) NOT NULL,
  namespace     text         NOT NULL,
  key           text         NOT NULL,
  value         jsonb        NOT NULL,
  updated_at    timestamptz  NOT NULL DEFAULT now(),
  PRIMARY KEY (feed_id, namespace, key),
  FOREIGN KEY (feed_id) REFERENCES feed(id) ON DELETE CASCADE,
  FOREIGN KEY (namespace, key) REFERENCES config_key(namespace, key) ON DELETE CASCADE
);

-- Helpful index
CREATE INDEX config_value_feed_gin ON config_value_feed USING GIN (value);