OTT-1418: use 6xx error code for openwrap NBR

[pm-nilesh-chate]

Description

Please add change description or link to ticket, docs, etc.

Checklist:

• PR commit list is unique (rebase/pull with the origin branch to keep master clean).
• JIRA number is added in the PR title and the commit message.
• Updated the header-bidding repo with appropiate commit id.
• Documented the new changes.

For Prebid upgrade, refer: https://inside.pubmatic.com:8443/confluence/display/Products/Prebid-server+upgrade

[ShriprasadM]

LGTM.
In future, If prebid came up with their own NBR codes, which starts conflicting with 6xx then we should prefer prebid standard NBR cod and should depreciate 6xx code.