accounts: Add credit and debit account functionality

[ViktorTigerstrom]

Fixes #648

This PR adds the actual RPC server implementation and exposes the functionality to credit or debit an account by a given amount.

This PR also introduces a depreciation warning for the litcli accounts update --new_balance flag.

[bitromortac]

Nice work, this will be useful and safer than the current approach 👍.

I tested a bit and found that the following works (although one is only able to credit and debit with the rpcs in the intended directions, so no sign change is possible).

No change (due to overflow):
litcli.sh accounts credit account_id 9223372036854775808

Credit X sat:
litcli.sh accounts credit account_id 9223372036854775808 + X

Debit X sat:
litcli.sh accounts debit account_id 9223372036854775808 + X

Maybe we want to prevent this on the RPC level?

Edit: not sure it's possible to detect as that may depend on the flag library

[ViktorTigerstrom]

Thanks a lot for the review @bitromortac!

Edit: not sure it's possible to detect as that may depend on the flag library

As also discussed offline earlier: Yeah I'm not sure there's anything we could do to avoid that issue unfortunately :/. But thanks a lot for testing this and good spotting of the issue!

[bitromortac]

LGTM ⚡

[lightninglabs-deploy]

@ViktorTigerstrom, remember to re-request review from reviewers when ready

[ViktorTigerstrom]

Thanks for the reviews @bitromortac & @ellemouton! I've addressed your feedback with the latest push :)

[ellemouton]

looking good! basically g2g

[ViktorTigerstrom]

Thanks for the review @ellemouton! I've addressed your comments in the latest push :)

[ellemouton]

Looks good! Final suggestion I promise :) what do you think of moving the new commands to rather be sub-commands of the update command? that way we keep things organised.

litcli.patch

[ViktorTigerstrom]

Looks good! Final suggestion I promise :) what do you think of moving the new commands to rather be sub-commands of the update command? that way we keep things organised.

litcli.patch

Cool thanks :)! I've updated the PR to address your feedback. Just a question of how we actually will implement the deprecation, as this will be my first time doing so:
In v16.0, will we just remote the account_balance field in the UpdateAccountRequest proto, and then also remove the new_balance argument in the litcli update command?

[ellemouton]

LGTM! Great work 🙏

Just a question of how we actually will implement the deprecation, as this will be my first time doing so:
In v16.0, will we just remote the account_balance field in the UpdateAccountRequest proto, and then also remove the new_balance argument in the litcli update command?

good question - tbh I think it's sort of up to us here cause: in LND, i think we've only really ever marked things as deprecated but then never actually followed through with removing them. So I think it's up to us and it depends on how urgently we want it to be deprecated and also what we expect the usage of it to be.
For this, perhaps yes a 1 release cycle heads up is good enough. We can perhaps add an explicit Deprecation notice section in the release notes to make things way more clear. If users complain at some point that the 1 release cycle heads up was too short, then we can either revert the change temporarily or just take note of the feedback for future deprecations.