Add 's2sConfig.syncTimeout' option

Code changes: prebid/Prebid.js#7744
Related: prebid/Prebid.js#6354

dev-docs/publisher-api-reference/setConfig.md

@@ -472,6 +472,7 @@ The `s2sConfig` properties:
 | `endpoint` | Required | URL or Object | Defines the auction endpoint for the Prebid Server cluster.  See table below for object config properties. |
 | `syncEndpoint` | Required | URL or Object | Defines the cookie_sync endpoint for the Prebid Server cluster. See table below for object config properties. |
 | `userSyncLimit` | Optional | Integer | Max number of userSync URLs that can be executed by Prebid Server cookie_sync per request.  If not defined, PBS will execute all userSync URLs included in the request. |
+| `syncTimeout` | Optional | Integer | Maximum number of milliseconds allowed for each userSync to load |
 | `coopSync` | Optional | Boolean | Whether or not PBS is allowed to perform "cooperative syncing" for bidders not on this page. Publishers help each other improve match rates by allowing this. Default is true. |
 | `defaultTtl` | Optional | Integer | Configures the default TTL in the Prebid Server adapter to use when Prebid Server does not return a bid TTL - 60 if not set |
 | `adapterOptions` | Optional | Object | Arguments will be added to resulting OpenRTB payload to Prebid Server in every impression object at request.imp[].ext.BIDDER. See the example above. |