add responseType to beachfront bidder params (prebid#2530)

Co-authored-by: John Salis <[email protected]>

dev-docs/bidders/beachfront.md

@@ -40,6 +40,7 @@ For further information, please contact [email protected].
 | `appId`          | optional | Beachfront Exchange ID for video bids. | `'11bc5dd5-7421-4dd8-c926-40fa653bec76'` | `string` |
 | `bidfloor`       | optional | Bid floor for video bids. | `0.01` | `float` |
 | `tagid`          | optional | Tag ID | `'7cd7a7b4-ef3f-4aeb-9565-3627f255fa10'` | `string` |
+| `responseType`   | optional | Video response type.<br/>`both`: VAST URL and VAST XML<br/>`nurl`: VAST URL only<br/>`adm`: VAST XML only | `'both'` | `string` |
 | `mimes`          | optional | Array of strings listing supported MIME types. | `["video/mp4", "application/javascript"]` | `Array<string>` |
 | `playbackmethod` | optional | Playback method supported by the publisher.<br/>`1`: Auto-play sound on<br/>`2`: Auto-play sound off<br/>`3`: Click-to-play<br/>`4`: Mouse-over | `1` | `integer` |
 | `maxduration`    | optional | Maximum video ad duration in seconds. | `30` | `integer` |