Alliance gravity: added PBS support (#6547)

* misc: added PBS support & changed parameter name

* misc: reverted parameter name

* fix: dummy commit

* fix(md): h3 to h2 header

Author: danielbaud

dev-docs/bidders/alliance_gravity.md

@@ -13,17 +13,17 @@ deals_supported: true
 floors_supported: true
 fpd_supported: false
 pbjs: true
-pbs: false
+pbs: true
 pbs_app_supported: true
 prebid_member: false
 multiformat_supported: will-bid-on-one
 ortb_blocking_supported: true
 privacy_sandbox: no
 ---
 
-### Bid Params
+## Bid Params
 
 {: .table .table-bordered .table-striped }
-| Name          | Scope    | Description       | Example   | Type     |
-|---------------|----------|-------------------|-----------|----------|
-| `srid`        | required | Stored Request ID | `'1234'` | `string` |
+| Name   | Scope    | Description  | Example  | Type     |
+|--------|----------|--------------|----------|----------|
+| `srid` | required | Placement ID | `'1234'` | `string` |