[F108] add locally produced blocks to checked_headers

[peterjah]

• document all added functions
• try in sandbox /simulation/labnet
  • if part of node-launch, checked using the resync_check flag
• unit tests on the added/changed features
  • make tests compile
  • make tests pass
• add logs allowing easy debugging in case the changes caused problems
• if the API has changed, update the API specification

[Leo-Besancon]

Aside from the fact that we insert twice non-local blocks into the cache (both during note_header_from_peer and in the added path here), the fix looks good.
Alternatives would probably require more changes to the codebase to cover all behaviors so that would not be worth it.

So the current PR LGTM!