[usage] Persist credits used for each instance in the usage store

[andrew-farries]

Description

Calculate and persist credits used for each instance in the usage store.

On each usage reconciliation run, we store the reconciled usage in the database. This information should include the number of credits consumed by each instance.

Previously, this value was set to 0 for all instances.

Related Issue(s)

Part of #10323

How to test

Unit tests.

To test manually, run the usage component locally against the database from a preview environment that has had at least one workspace started in it. When the reconciler runs, see that the value for creditsUsed is populated in the d_b_workspace_instance_usage table:

Release Notes

NONE

Documentation

Werft options:

• /werft with-preview

[werft-gitpod-dev-com]

started the job as gitpod-build-af-persist-credits-used-in-usage-store.1 because the annotations in the pull request description changed
(with .werft/ from main)

[geropl]

about the float64: I faintly recall we report credits as ints to stripe, right? If yes, we probably should do the same here, and adjust the DB/gRPC model if they don't agree.

@andrew-farries WDYT?

[andrew-farries]

The designs here internal show credits displayed with fractions.

But I think you are right in that we should be consistent in allowing the credits per minute for a workspace class be fractional but always bill and display whole numbers of credits.

I'll update the types in a follow-up.

[jldec]

My understanding was that we have to report total usage to Stripe as an int, but we should collect usage per session in fractional units to avoid rounding errors.

[andrew-farries]

As explained here, @jldec is right in thinking that this should in fact remain a float.

[geropl]

Nice! Really cool to see the piece snap together 🙃

/hold because of float vs int question. We can also do that as a follwo-up 👍

[andrew-farries]

/unhold