Refactor inactive-blog-filter.js to use Redis vs. files

[humphd]

We have some logic that is using files to deal with state, and we need to move that into Redis, so it can be distributed across nodes in production.

The various files that are being used in inactive-blog-filter.js should be refactored to use Sets in Redis, which we should be able to use to do set operations (unions, diffs, intersections, etc), and thereby keep our list of feeds up to date.

See the code in storage.js for some ideas on how to do this. We'll need to add more code there for this use case.

[Silvyre]

Please allow me!

[Silvyre]

Stepping aside from this to assist with #406. Anyone is welcome to take my place.

[haichuan0424]

Karla and I are going to do this.

[haichuan0424]

Going to take #270 instead. Feel free to take this.

[c3ho]

If someone is not taking this, I think I can work on it too, since there is some dependency from #462 on this.

[c3ho]

This depends on changes from #462

[c3ho]

async function check(feedUrl, redlistPath = 'feeds-redlist.json') {
  // Read redlist file
  try {
    const redListRaw = await fsPromises.readFile(redlistPath, 'utf-8');
    const redList = [].concat(JSON.parse(redListRaw));
    return redList.some(redItem => isRedlisted(feedUrl, redItem));
  } catch (error) {
    logger.error({ error }, `failed to read ${redlistPath}`);
    throw error;
  }
}

@humphd Most of the code in in inactive-blog-filter is using a feedUrl, did you want to change to using a feedId here instead?

[humphd]

I want to get rid of this code completely, and use the the invalid key concept with a feed id like I mentioned in the other comments I left.

[c3ho]

Closing this as it was addressed by #630