itest: Add custom channels with grouped asset test

[GeorgeTsagk]

Description

This PR adds a new itest that uses a grouped asset, in order to tackle some of the issues discovered in lightninglabs/taproot-assets#947

Closes lightninglabs/taproot-assets#957

[guggero]

Looks like the grouped asset itest fails consistently when sending a payment. Does that happen as well for you locally?

[GeorgeTsagk]

Looks like the grouped asset itest fails consistently when sending a payment. Does that happen as well for you locally?

Nope, locally it passes consistently, and on Github CI it's flaky

[guggero]

The flake will be fixed by lightningnetwork/lnd#8871. Not sure if we should get this in while flakey and then wait for the CI to become fully green in #782 which bumps all dependencies?

[guggero]

LGTM 🎉

I'm in favor of merging this, even if the itest doesn't pass yet. I've confirmed that lightningnetwork/lnd#8871 will fix this, so it's just a matter of bumping the lnd dependency after merge, which #782 will do anyway.

[GeorgeTsagk]

The flake will be fixed by lightningnetwork/lnd#8871. Not sure if we should get this in while flakey and then wait for the CI to become fully green in #782 which bumps all dependencies?

I'm fine both ways, since we know it's a flake we could hit the merge prematurely