feat: use DualCurrency input field (#35)

[hvoecking]

I deviated a bit from the screenshot of #35 to make the implementation of #44 easier. Another reason is that the displayed value in USD is only the current equivalent, in the future it might have a different value of course, so I expressed that accordingly.

I could not find any tests, so I have not added any for this new feature as introducing all of the testing infrastructure would be out of scope of this PR. But I'm happy to add them once testing is in place.

Two more things, when running locally I got the following error:

- error pages/api/inngest.ts (16:13) @ eval
- error Error [TypeError]: Cannot set property crypto of #<Object> which has only a getter
    at eval (webpack-internal:///(api)/./pages/api/inngest.ts:50:15)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
  digest: undefined
}
  14 | import ms from "ms";
  15 |
> 16 | global.crypto = crypto;
     |             ^
  17 |
  18 | type PeriodicZapEvent = {
  19 |   name: "zap";

Another problem was that I had to change the serveHost in pages/api/inngest.ts to "http://localhost:8081" for it to run locally. But since these issues are unrelated to this PR I did not touch them. Just FYI

[rolznz]

@hvoecking thanks for your PR and sorry for the delay! those issues you had have been fixed locally.