Intent of TestWithTags_DistinguishesEmbeddedNullTags

All 8 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 8 tests
- server/ 8 tests
  - common/ 8 tests
    
    metrics/ 8 tests
    
    go.temporal.io/server/common/metrics/TestScopeCache_IndependentPerHandler Inherited TestScopeCache_IndependentPerHandler
    
    go.temporal.io/server/common/metrics/TestTallyScope Inherited TestTallyScope
    
    go.temporal.io/server/common/metrics/TestWithTags_CachedHandlerRecordsMetricsCorrectly Inherited TestWithTags_CachedHandlerRecordsMetricsCorrectly
    
    go.temporal.io/server/common/metrics/TestWithTags_ChildCachesAreIndependent Inherited TestWithTags_ChildCachesAreIndependent
    
    go.temporal.io/server/common/metrics/TestWithTags_DifferentTagsReturnDifferentHandlers Inherited TestWithTags_DifferentTagsReturnDifferentHandlers
    
    go.temporal.io/server/common/metrics/TestWithTags_DistinguishesEmbeddedNullTags Introduced here
    
    go.temporal.io/server/common/metrics/TestWithTags_MultipleTagsCacheCorrectly Inherited TestWithTags_MultipleTagsCacheCorrectly
    
    go.temporal.io/server/common/metrics/TestWithTags_TagOrderMatters Inherited TestWithTags_TagOrderMatters