Add skip media during sync option for faster history sync completion

[fru-9D]

Overview

This PR introduces a new configuration option skip_media_during_sync that allows users to skip media downloads during initial history sync for significantly faster completion times.

Problem

History sync can be slow and resource-intensive, especially for users with large chat histories containing many media files. The media download process during sync can significantly delay the completion of initial sync.

Solution

• New Configuration: Added skip_media_during_sync boolean option in the history_sync section
• Context-Aware Media Handling: Modified media processing to skip downloads when the option is enabled during backfill
• Manual Media Recovery: Users can still request historical media manually through the existing media retry system

Key Changes

Configuration (config.go, example-config.yaml)

• Added SkipMediaDuringSync bool field to HistorySync config struct
• Updated config upgrade function to handle the new field
• Added documentation in example config

Media Processing (wa-media.go)

• Modified reuploadWhatsAppAttachment() to check for is_backfill and skip_media context values
• When both conditions are true, the function returns early without downloading/uploading media

Backfill Context (backfill.go)

• Enhanced convertHistorySyncMessage() to set backfill context with is_backfill: true and skip_media: [config value]
• Updated ToMatrix() call to include the new isBackfill parameter

Benefits

1. Faster Sync Completion: Significantly reduces initial sync time by skipping media downloads
2. Reduced Resource Usage: Lower bandwidth and storage requirements during sync
3. Better User Experience: Users can start using the bridge sooner
4. Backward Compatible: Existing functionality remains unchanged when the option is disabled

Configuration Example

history_sync:
  skip_media_during_sync: true  # Skip media during initial sync for faster completion

Migration

No database migration required. The new configuration option defaults to false to maintain existing behavior for existing installations.

[tulir]

This doesn't look very useful as the media will be lost forever. Async uploads and direct media already exist for making media faster