fix(databases): parseScheduleAtFlag returns a validation error

[EtienneM]

The error message is now clearer if the client does not provide a good format. For example:

 bsscalingo --app biniou backups-config --addon postgresql --schedule-at "azerty UTC"
 !     An error occurred:
       schedule-at=first field must be a digit representing the hour

And I updated the parsing function to be compatible with 4:00 (and not only 4).

Fix #1106

• Add a changelog entry in the section "To Be Released" of CHANGELOG.md

[sc-zenokerr]

A suggestion otherwise LGTM.

[sc-zenokerr]

Question, do we want to be prescriptive or accommodating about the format allowed?

If we allow 4 and 4:00 do we want to allow 04 and 04:00 or 4h and 4h00 etc... where is the line drawn.

If we want to be accommodating I would suggest replacing the scheduleAtTimeSplit with something more general, such as:

re := regexp.MustCompile(`([:hH].*)|[0]+`)
scheduleAtHour, err := strconv.Atoi(re.ReplaceAllString(scheduleAtTime, ""))

as this would accommodate lots of different formats e.g:

		"4",
		"4h",
		"4H",
		"04h",
		"4:00",
		"4:12",
		"04:00",
		"04:12",
		"09:00",
		"09",
		"4h:45",

I made a goplayground here to test this for myself: https://go.dev/play/p/UxHf9xVmiCJ

[EtienneM]

Great idea, thanks. Done in 40bdb7d. I also took the opportunity to add a unit test for parseScheduleAtFlag to ensure we don't break anything.

[sc-zenokerr]

LGTM. Thanks :)