Nexx360: ext usage added for imp and gvlVendorID added

[gchicoye]

We've added functionality to manage imp.ext fields and added gvlVendorID: 965 to bidder-info

[github-actions]

Code coverage summary

Note:

• Prebid team doesn't anticipate tests covering code paths that might result in marshal and unmarshal errors
• Coverage summary encompasses all commits leading up to the latest one, f2df44b

nexx360

Refer here for heat map coverage report

github.com/prebid/prebid-server/v3/adapters/nexx360/nexx360.go:43:	Builder		100.0%
github.com/prebid/prebid-server/v3/adapters/nexx360/nexx360.go:50:	getVersion	66.7%
github.com/prebid/prebid-server/v3/adapters/nexx360/nexx360.go:59:	processImps	84.6%
github.com/prebid/prebid-server/v3/adapters/nexx360/nexx360.go:114:	makeReqExt	100.0%
github.com/prebid/prebid-server/v3/adapters/nexx360/nexx360.go:124:	MakeRequests	88.0%
github.com/prebid/prebid-server/v3/adapters/nexx360/nexx360.go:177:	MakeBids	100.0%
github.com/prebid/prebid-server/v3/adapters/nexx360/nexx360.go:222:	getBidType	100.0%
total:									(statements)	91.3%