wire+chaincfg: add signet params

[guggero]

This commit adds all necessary chain parameters for connecting to the
public signet network.
Reference: bitcoin/bitcoin#18267

Needed for adding signet support to lnd.
Replaces #1536.

cc @Roasbeef, @cfromknecht.

[coveralls]

Pull Request Test Coverage Report for Build 773968254

• 90 of 131 (68.7%) changed or added relevant lines in 3 files are covered.
• 12 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.06%) to 52.916%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
rpcserver.go	0	2	0.0%
config.go	0	39	0.0%

Files with Coverage Reduction	New Missed Lines	%
peer/peer.go	12	75.47%

Totals
Change from base Build 745866572:	0.06%
Covered Lines:	21017
Relevant Lines:	39718

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💛 - Coveralls

[guggero]

cc @wpaulino

[Roasbeef]

How about the ability to configure a signet target at runtime? Otherwise if people want to make their own custom signets (which I think is the whole point?), then they'd need to recompile and distribute their binaries, vs being able to say: "yo use these params to join my signet that has covenants implemented".

[guggero]

@Roasbeef I added the changes necessary to connect to a custom signet. I wasn't able to spin one up locally, but I'll test this as soon as I'm successful.

[guggero]

I've verified that syncing a btcd node against both the "public taproot signet" and a custom local signet work.

Example for connecting to a custom local signet (using bitcoind, see script below):

btcd --signet --signetchallenge=512103e5602bf0701c1565a89695eb618c3d652b0532464dbfca6130c659c06dfc11fd51ae --signetseednode=127.0.0.1 --listen=:38666 --rpclisten=:38662 --rpcuser=lightning --rpcpass=lightning

Client:

btcctl --signet --rpccert ~/.btcd/rpc.cert --rpcuser=lightning --rpcpass=lightning --rpcserver=localhost:38662

Here's my script I used to spin up my own signet (must run inside the src directory of the bitcoin source code with the current master compiled): https://pastebin.com/YJKAPM0p

[guggero]

@Roasbeef PTAL, would be nice to include this in the next lnd release.

[Roasbeef]

Thanks for making the signet configuration more flexible! I have some things in mind that would be really dope to expose using a new public signet 😈

[Roasbeef]

@guggero tried to click on that pastebin link but it's expired, if you recall what it was, can you re-host it somewhere? Thanks!

[Roasbeef]

Actually re-visiting the BIP, this doesn't appear to allow creation of a "custom" signet as no new logic to validate the new block commitment nor the challenge signature has been added. Is the intent here just to add a "light" minimally validating signet client in the short term before following up w/ the proper block generation and validation logic?

[Roasbeef]

Chatted w/ Oliver offline and determined that we'll merge this "light client" functionality, then later follow up with the fully logic needed to produce and verify signet blocks so new public btcd based signets will be possible in the future.