Generate weekly Slack report for projects in the org with configurable channel selection

[Copilot]

This PR implements a weekly Slack report feature that automatically sends comprehensive project and repository statistics to organizations with Slack integration.

Changes Made

1. Management Command (slack_weekly_report.py)

Created a Django management command that generates and sends weekly reports including:

• Overview Statistics: Total projects, repositories (active/archived breakdown)
• Aggregate Metrics: Total stars, forks, open issues, and contributors across all repos
• Recently Updated Repositories: Top 10 repos updated in the last 7 days
• Project Breakdowns: Detailed information about projects with repository counts and status

The command uses efficient Django ORM queries with aggregates and annotations to prevent N+1 query problems and is timezone-aware for consistent datetime operations.

2. Weekly Cron Command (run_weekly.py)

Updated the existing run_weekly.py command to:

• Call the slack_weekly_report command
• Follow the pattern from run_daily.py and run_hourly.py for consistency
• Allow easy addition of other weekly commands in the future
• Provide proper error handling and logging for weekly scheduled tasks

3. Configurable Report Channel

Added new fields to SlackIntegration model:

• weekly_report_channel_name: Optional channel name for weekly reports
• weekly_report_channel_id: Optional channel ID for weekly reports
• Falls back to default_channel_id if weekly report channel is not configured
• Allows organizations to send weekly reports to a dedicated channel separate from daily updates or other notifications

4. GitHub Actions Workflow (weekly-slack-report.yml)

Created an automated workflow that:

• Runs every Saturday at 1pm EST (6pm UTC) using cron schedule: '0 18 * * 6'
• Calls the run_weekly command which executes all weekly scheduled tasks
• Can be manually triggered via workflow_dispatch for testing
• Sets up the required environment (PostgreSQL, Python 3.11, Poetry)

5. Tests (test_slack.py)

Added comprehensive test coverage for the weekly report functionality:

• Tests report generation and successful message sending
• Tests report content with and without projects
• Tests custom channel configuration
• Tests fallback to default channel behavior
• Proper mocking of Slack API interactions with specific module path patches

Technical Optimizations

• Single aggregate query with Q filters for efficient repo counting
• Count annotation for project repo counts (prevents N+1 queries)
• Configurable limits via class constants (MAX_RECENT_REPOS, MAX_PROJECTS_IN_REPORT, MAX_DESCRIPTION_LENGTH)

How It Works

The report is automatically sent to all organizations that have a Slack integration configured. Organizations can:

1. Use the default channel for all Slack notifications (by not setting weekly_report_channel_id)
2. Configure a specific channel for weekly reports (by setting weekly_report_channel_id and optionally weekly_report_channel_name)

The workflow runs the centralized run_weekly command, making it easy to add additional weekly scheduled tasks in the future.

• Fixes OWASP-BLT/BLT#2484

Original prompt

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This section details on the original issue you should resolve

<issue_title>Generate a report that is sent to Slack Saturday at 1pm EST - weekly slack report of projects in the org </issue_title> <issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes OWASP-BLT/BLT#2484

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