Do not break dashboard settings UI when time intervals end with trailing comma

[dprokop]

Fixes #26097

Done:

1. Time intervals input is controlled now and change is propagated on blur
2. SettingsCtrl makes sure saved refresh intervals do not contain empty values

[torkelo]

Looks good, we have some other strange problems with the interval options, like
#25842

[dprokop]

Looks good, we have some other strange problems with the interval options, like #25842

@torkelo yeah, that one is really strange and I got confused as well:D But at the same time it's a consequence of the configuration, so the question is - do we want the user-configured intervals to override the config? Currently, it's an inclusive relation - whatever is configured in the min_refresh_interval lands in the refresh picker ¯_(ツ)_/¯

I would expect and I think that whatever the user put into the refresh intervals settings should take precedence over any other settings.