[dashboard] Fix display of billing period boundaries by using only UTC times

[jankeromnes]

Description

Fix display of billing period boundaries in the dashboard by using only UTC times.

(Note: I did try to use dayjs for this, but couldn't figure out how to "force" everything to be UTC, so I fell back on the native Date type. Happy to switch to dayjs if you know how to achieve exactly the same result. 👍)

Related Issue(s)

Fixes #

How to test

1. Upgrade to usage-based billing
2. Billing period boundaries shown in your billing UI should be correct

Release Notes

NONE

Documentation

Werft options:

• /werft with-local-preview
  If enabled this will build install/preview
• /werft with-preview
• /werft with-payment
• /werft with-integration-tests=all
  Valid options are all, workspace, webapp, ide

[werft-gitpod-dev-com]

started the job as gitpod-build-jx-fix-billing-period-ui.1 because the annotations in the pull request description changed
(with .werft/ from main)

[easyCZ]

To use dayjs, we can use https://day.js.org/docs/en/manipulate/utc
It would look like this: https://github.com/gitpod-io/gitpod/pull/14100/files

[jankeromnes]

Many thanks @easyCZ for taking the time to propose a dayjs alternative PR! 🙏

I'll take a look at your proposed changes, and pull them in if I see no issue with them. 👍

[werft-gitpod-dev-com]

started the job as gitpod-build-jx-fix-billing-period-ui.4 because the annotations in the pull request description changed
(with .werft/ from main)

[werft-gitpod-dev-com]

started the job as gitpod-build-jx-fix-billing-period-ui.5 because the annotations in the pull request description changed
(with .werft/ from main)

[easyCZ]

LGTM 😉