Exclude well-known empty entities

[lidel]

Adding /ipfs/QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn (empty unixfs dir) bricks Kubo, daemon is unable to start:

2023-10-19T19:51:49.062+0200	WARN	nopfs	nopfs@v0.0.12-0.20231012170252-ab19c8a36941/denylist.go:169	Opening /home/lidel/tmp/ttl-ipns-repo/denylists/text.deny: empty header
2023-10-19T19:51:49.063+0200	INFO	nopfs	nopfs@v0.0.12-0.20231012170252-ab19c8a36941/denylist.go:170	Processing /home/lidel/tmp/ttl-ipns-repo/denylists/text.deny: text.deny (No header found) by unknown
2023-10-19T19:51:49.063+0200	DEBUG	nopfs	nopfs@v0.0.12-0.20231012170252-ab19c8a36941/denylist.go:431	text.deny:1: IPFS rule. Key: QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn. Entry: Path: (empty). Prefix: false. AllowRule: false.
2023-10-19T19:51:49.063+0200	DEBUG	nopfs	nopfs@v0.0.12-0.20231012170252-ab19c8a36941/denylist.go:783	IsCidBlocked load: QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn
2023-10-19T19:51:49.063+0200	DEBUG	nopfs	nopfs@v0.0.12-0.20231012170252-ab19c8a36941/entry.go:38	check-path:  matches
2023-10-19T19:51:49.063+0200	ERROR	core	core/builder.go:158	constructing the node: could not build arguments for function "reflect".makeFuncStub (reflect/asm_amd64.s:28): failed to build *mfs.Root: received non-nil error from function "github.com/ipfs/kubo/core/node".Files (github.com/ipfs/kubo/core/node/core.go:136): failure writing to dagstore: QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn is blocked and cannot be provided

Error: constructing the node (see log for full detail): failure writing to dagstore: QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn is blocked and cannot be provided

In practice, there is a short set of well-known empty CIDs that should never be blocked:

• empty unixfs directory
  • QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn
  • bafyaabakaieac (inlined)
• empty block
  • raw: bafkreihdwdcefgh4dqkjv67uzcmw7ojee6xedzdetojuzjevtenxquvyku
  • inlined raw: bafkqaaa
  • dag-pb: QmbFMke1KXqnYyBBWxB74N4c5SBnJMVAiMNRcGu6x1AwQH
  • dag-cbor: bafyreigbtj4x7ip5legnfznufuopl4sg4knzc2cof6duas4b3q2fy6swua
  • dag-json: baguqeeraiqjw7i2vwntyuekgvulpp2det2kpwt6cd7tx5ayqybqpmhfk76fa

@hsanjuan thoughts? would it be feasible to keep a safelist that overrides denylists, or are we ok with the footgun? (feature, not a bug)

[hsanjuan]

I think it should be ok to ignore these if they appear when parsing the denylist.