Add InitialFetchCount and Onward Date to populate Forums

[talDoFlemis]

Overview

This PR introduces a new optional feature that allows FeedCord to backfill recent posts when a feed worker first initializes. This is useful for populating a Discord channel with recent content when setting up a new feed instance, rather than only posting new items that arrive after initialization.

New Features

1. Initial Fetch Count (InitialFetchCount)

A new optional configuration property that specifies how many of the most recent posts to fetch when the feed worker first initializes.

Default Value: 0 (disabled)

2. Onward Date Filter (OnwardDate)

A new optional configuration property that works in conjunction with InitialFetchCount to filter posts by publish date.

Default Value: null (no date filtering)

Configuration Examples

Example 1: Basic Initial Fetch

Fetch the last 10 posts without date filtering:

{
  "Instances": [
    {
      "Id": "Tech News",
      "YoutubeUrls": [""],
      "RssUrls": ["https://example.com/feed.rss"],
      "DiscordWebhookUrl": "https://discord.com/api/webhooks/...",
      "RssCheckIntervalMinutes": 15,
      "Color": 8411391,
      "DescriptionLimit": 500,
      "Forum": true,
      "MarkdownFormat": false,
      "PersistenceOnShutdown": true,
      "InitialFetchCount": 10
    }
  ],
  "ConcurrentRequests": 40
}

Example 2: Date-Filtered Initial Fetch

Fetch up to 20 recent posts, but only those published after November 1st, 2025:

{
  "Instances": [
    {
      "Id": "Tech News",
      "YoutubeUrls": [""],
      "RssUrls": ["https://example.com/feed.rss"],
      "DiscordWebhookUrl": "https://discord.com/api/webhooks/...",
      "RssCheckIntervalMinutes": 15,
      "Color": 8411391,
      "DescriptionLimit": 500,
      "Forum": true,
      "MarkdownFormat": false,
      "PersistenceOnShutdown": true,
      "InitialFetchCount": 20,
      "OnwardDate": "2025-11-01T00:00:00"
    }
  ],
  "ConcurrentRequests": 40
}

Example 3: Default Behavior (No Backfill)

When InitialFetchCount is omitted or set to 0, FeedCord operates as it always has:

{
  "Instances": [
    {
      "Id": "Tech News",
      "YoutubeUrls": [""],
      "RssUrls": ["https://example.com/feed.rss"],
      "DiscordWebhookUrl": "https://discord.com/api/webhooks/...",
      "RssCheckIntervalMinutes": 15,
      "Color": 8411391,
      "DescriptionLimit": 500,
      "Forum": true,
      "MarkdownFormat": false,
      "PersistenceOnShutdown": true
    }
  ],
  "ConcurrentRequests": 40
}

Documentation Updates

• Updated README.md with the new properties in the configuration example