TimeframeForm: Use localDateTime instead of Flatpickr

[jhoxhaa]

fix #128

[lippserd]

@jhoxhaa Please rebase and resolve merge conflicts.

Does the textual datetime description still work? For example -1 hour.

[jhoxhaa]

With this, a textual input is only allowed for start and end simultaneously. A fixed datetime for end only doesn't make much sense, but for start. Consider a report that covers results since 01-01-2022 00:00:00. Of course, this is the same as the default timeframe Current Year, just expressed differently, but it shows that this example is not unreasonable. I'd opt for both expressions as a fixed date is more comprehensible as such a relative expression: first day of January this year midnight. (Especially easier to input, with the help of a widget) Though, wait for @lippserd's opinion before changing this.

Do you mean we should use fixed datetime only or that we should be able to use both expressions at the same time? 🤔

[nilmerg]

Currently it's only fixed + fixed or relative + relative, what I'd like to have is: fixed + relative

[yhabteab]

Once this is ready, please make sure that this issue doesn't occur anymore!

• https://github.com/Icinga/icingaweb2-module-reporting/issues/172