chore(types): document which types are user-facing

[jamietanna]

For instance, packageFiles with updates will log

renovate/lib/workers/repository/process/extract-update.ts

Line 229 in d2493d0

packageFiles: Record<string, PackageFile[]>,

which contains within it updates?: LookupUpdate[];

As found in #42311, the addition of hasAttestation results in to LookupUpdate results in it appearing in packageFiles with updates.

This isn't a problem, but it's worth making it clear to ourselves for future changes what is/is not user-facing

We should:

• document with JSDoc/an annotation what will be logged
• potentially add an allowlist of fields we want to expose
  • i.e. it might be that we don't want mergeConfidenceLevel logged (even though it appears on the type, it's only set when matchConfidence is used)