CBG-3518: Conditional logging for DocChanged based on collection ID

[bbrks]

CBG-3518

Tweak logging from DocChanged for collections

• Include KV Collection ID in log lines where we don't recognise the collection (too expensive to lookup collection name from here)
• Add collection name context to all DocChanged logging when we're able to determine it
• Drop warning to debug and reword when it's an expected condition (DocChange events from another database's _default collection that we want to ignore)
• Allow AssertLogContains helper to "tee" logs with a MultiWriter to prevent logs going silent during assertions.

Examples:

2023-10-09T17:58:04.542+01:00 [DBG] Changes+: t:TestDocChangedLogging db:db col:sg_test_0 Received #1 after   0ms ("<ud>doc1</ud>" / "1-cd809becc169215072fd567eebd8b8de")
2023-10-09T17:58:04.542+01:00 [DBG] Changes+: t:TestDocChangedLogging db:db col:sg_test_1 Received #2 after   0ms ("<ud>doc1</ud>" / "1-cd809becc169215072fd567eebd8b8de")
2023-10-09T17:58:04.543+01:00 [DBG] Cache+: t:TestDocChangedLogging db:db DocChanged(): Ignoring non-metadata mutation for doc "<ud>doc1</ud>" in the default collection - kv ID: 0

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/000/