Update the public ChannelMetadata viewset to support token filter

[taoerman]

Summary

Implements token-based filtering for the ChannelMetadataViewSet (v2 public API). Previously, token-based channel lookup was only available through the v1 endpoint (get_public_channel_lookup). This change brings that functionality to the v2 API with support for both Channel tokens and ChannelVersion tokens.

• The ChannelMetadataViewSet now has support for token filtering
• Returns adequate values for channel tokens
• Returns adequate values for channel version tokens (with version-specific published_size)
• New unit tests added to ensure token filtering works correctly
• New unit tests verify other filters keep working when no token is provided

References

Fixed #5462

Reviewer guidance

Run Unit Tests