Docs/update missena params (#6136)

* New Prebid Server Adapter: Missena

* set prebid_member to true

* Add pbs: true to the metadata

* Update Missena bidder docs with formats and settings parameters

* Enhance Missena bidder documentation with available placement values

Author: ysfbsf

dev-docs/bidders/missena.md

@@ -25,3 +25,13 @@ The Missena Bidding adapter requires setup before beginning. Please contact us a
 | `placement`   | optional | Placement Type, default: 'sticky' | `'sticky'` | `string` |
 | `formats`  | optional | An array of formats to request (banner, native, or video) | `['banner', 'video']` | `array` |
 | `settings` | optional | An object containing extra settings for the Missena adapter | `{ settingName: 'value' }` | `object` |
+
+#### Available Placement Values
+
+The `placement` parameter accepts the following values:
+
+- `sticky` - Default sticky placement
+- `header` - Header placement
+- `footer` - Static footer placement
+- `prestitial` - Full-screen ad before content loads
+- `postitial` - Full-screen ad after content loads