cluster: fix cloud storage self-test start/end time output

[WillemKauf]

The start/end times for tests ran with the self-test tool were recently added to the output of rpk config self-test status.

These times were not being set in the cloud storage self-test, and thus the START and END times would both be epoch time, i.e

NAME          Cloud Storage Test
INFO          Put
TYPE          cloud
TEST ID       2cf3b181-3cb8-4502-a987-28dfd60f4f12
TIMEOUTS      0
START TIME    Thu Jan  1 00:00:00 UTC 1970
END TIME      Thu Jan  1 00:00:00 UTC 1970
AVG DURATION  7ms

This PR fixes the start and end time outputted for the result of the test, for either failed or successful tests.

NAME          Cloud Storage Test
INFO          Put
TYPE          cloud
TEST ID       0d40dc63-5a7f-43df-b175-de33411d1df9
TIMEOUTS      0
START TIME    Fri July  12 16:00:13 UTC 2024
END TIME      Fri July  12 16:00:13 UTC 2024
AVG DURATION  7ms

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v24.1.x
• v23.3.x
• v23.2.x

Release Notes

Improvements

• Improve rpk cluster self-test status output for the cloud test.

[andrwng]

LGTM, this hasn't made its way to a release yet, has it?

[WillemKauf]

Force push to correct usage of ss::lowres_clock::now() to ss::lowres_system_clock::now().

[Deflaimun]

Thanks for the fix @WillemKauf. Have you added start/end regardless of test status ?
Asking because this might be helpful for debugging purposes.

[WillemKauf]

Thanks for the fix @WillemKauf. Have you added start/end regardless of test status ?

Asking because this might be helpful for debugging purposes.

Yes, start/end times will be outputted regardless of test failure/success.