OpenX: Determine bid type from bid.mtype

[gmiedlar-ox]

OpenX started to return mtype field for bids in bid response, so now bid type can be determined based on this property in OpenX bidder adapter.
We want to determine bid type based on bid mtype from bid response, to be able to process multi-format requests.

[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, 8b7c575

openx

Refer here for heat map coverage report

github.com/prebid/prebid-server/v3/adapters/openx/openx.go:35:	MakeRequests		100.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:76:	makeRequest		75.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:122:	preprocess		85.3%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:191:	MakeBids		87.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:247:	getBidVideo		100.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:258:	getBidType		100.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:278:	getMediaTypeForImp	88.9%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:294:	Builder			100.0%
total:								(statements)		88.0%

[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, 8b7c575

openx

Refer here for heat map coverage report

github.com/prebid/prebid-server/v3/adapters/openx/openx.go:35:	MakeRequests		100.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:76:	makeRequest		75.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:122:	preprocess		85.3%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:191:	MakeBids		87.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:247:	getBidVideo		100.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:258:	getBidType		100.0%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:278:	getMediaTypeForImp	88.9%
github.com/prebid/prebid-server/v3/adapters/openx/openx.go:294:	Builder			100.0%
total:								(statements)		88.0%

[bsardo]

@pm-shriprasad-marathe can you please review?