Add capacity to filter select client_name values

[stephen-soltesz]

This change adds support for filtering select client_name values from the ndt7 ClientMetadata. This change prevents the value from being published to BigQuery, making the value effectively unsearchable, though it will remain in the underlying raw storage. Since clients optionally provide the client_name value, it is impossible to distinguish between clients that never provided the value or those that have the value filtered without looking at the raw data directly.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 7433

• 32 of 35 (91.43%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 67.384%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/ndt7_result.go	32	35	91.43%
<!--	Total:	32	35	91.43%	-->

Files with Coverage Reduction	New Missed Lines	%
active/active.go	2	90.63%
<!--	Total:	2		-->

Totals
Change from base Build 7429:	0.2%
Covered Lines:	3351
Relevant Lines:	4973

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💛 - Coveralls

[stephen-soltesz]

Obsolete.