Use sat/msat arguments of ln addinvoice

[GeorgeTsagk]

Description

Uses the existing LND arguments for sat/msat amount for the litcli ln addinvoice command. This new argument exposes the behavior introduced in lightninglabs/taproot-assets#1448

Closes #1073

[guggero]

If you look at litcli ln addinvoice, you see that we already have all flags from commands.AddInvoiceCommand.Flags:

   --amt value                      the amt of satoshis in this invoice (default: 0)
   --amt_msat value                 the amt of millisatoshis in this invoice (default: 0)

So we should use those.

[GeorgeTsagk]

Thanks!

Also wondering why we do field related checks on the cmd level, as they are also checked in tapd/lnd

[GeorgeTsagk]

Ok realized the RPCs don't always return user-friendly errors, so made the checks in cmd too (much better to get a single text message back saying must only set X or Y)

[guggero]

tACK. While testing I found out that --amt doesn't work, only --amt_msat. But that needs to be fixed in tapd, which I'm going to do now.

[guggero]

Needs a rebase to get the itests running.

[GeorgeTsagk]

tACK. While testing I found out that --amt doesn't work, only --amt_msat. But that needs to be fixed in tapd, which I'm going to do now.

Ah! great catch, I believe I only tried amt_msat while testing locally and didn't run into it. Ty!

[guggero]

LOL, apparently if you use the "fixes" keyword and then link to another PR, that one is closed... Sorry, my bad.