Core: allow vast xml without using cache

[mkomorski]

Introduces new flag cache.allowVastXmlOnly which removes obligation of using cache (local or remote) with video bids

Type of change

• Bugfix

• Feature

• New bidder adapter

• Updated bidder adapter

• Code style update (formatting, local variables)

• Refactoring (no functional changes, no api changes)

• Build related changes

• CI related changes

• Does this change affect user-facing APIs or examples documented on http://prebid.org?

• Other

Description of change

Other information

fixes #14509

[coveralls]

Pull Request Test Coverage Report for Build 23249867750

Details

• 12 of 12 (100.0%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.001%) to 96.344%

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Files with Coverage Reduction	New Missed Lines	%
modules/adxpremiumAnalyticsAdapter.js	1	83.19%

Totals
Change from base Build 23229096016:	0.001%
Covered Lines:	215926
Relevant Lines:	224120

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💛 - Coveralls

[monis0395]

LGTM!

[karimMourra]

Thanks @mkomorski !