feat(bedrock): send documents and video on the Converse API (#1004)

* feat(bedrock): send documents and video on the Converse API

The Converse formatter dropped `file`, `image_url` and `video_url` parts, so
a PDF or a video never reached the model. They now become `document`, `image`
and `video` blocks chosen by media type or file extension, sourced from inline
bytes or an `s3://` location, with the document name taken from the part's
`title` metadata or its filename. Formats are sent as given for Amazon to
refuse; sources Converse cannot fetch raise instead of disappearing.

* fix(bedrock): validate Converse document requests

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Co-authored-by: Mike Hostetler <84222+mikehostetler@users.noreply.github.com>