Support TCF Policy Version 5

[bretg]

Related to #2697, apparently the IAB now has a TCF Policy v5

Versions 62 and 63 of the GVL have this new version -- https://vendor-list.consensu.org/v3/vendor-list.json

gvlSpecificationVersion:3
vendorListVersion:63
tcfPolicyVersion:5

This is causing Prebid Server to reject consent strings as invalid. So this is pretty urgent. Heads up @bsardo and @SyntaxNode .

Here are the proposed updates:

1. allow tcfPolicyVersion==5
2. Update the algorithm for setting gvlSpecificationVersion:
   1. If tcfPolicyVersion<4, set gvlSpecificationVersion=2
   2. If tcfPolicyVersion is in (4,5), set gvlSpecificationVersion=3
   3. otherwise, the incoming TCF string is invalid. Blank it out (no consent), emit an error in debug output, and log an error to the error log at N% sampling. The error should contain the value of the received tcfPolicyVersion.

[bretg]

Discussed in committee:

1. allow any tcfPolicyVersion, but emit alert.general metric if tcfPolicyVersion>5. At 1%, log a warning "unknown tcfPolicyVersion, defaulting to gvlSpecificationVersion=3"
2. Update the algorithm for setting gvlSpecificationVersion:
   1. If tcfPolicyVersion<4, set gvlSpecificationVersion=2
   2. If tcfPolicyVersion >=4, set gvlSpecificationVersion=3
   3. otherwise, the incoming TCF string is invalid. Blank it out (no consent), emit an error in debug output, and log an error to the error log at N% sampling. The error should contain the value of the received tcfPolicyVersion.

[bretg]

PBS-Java 3.8 will partly address this. 3.9 will address the more general solution.

[bsardo]

PBS-Go currently sets gvlSpecificationVersion=3 when tcfPolicyVersion >= 4. PBS-Go will just need to add the metric if tcfPolicyVersion>5.