Feat: Add options for Chart period

[chakflying]

Closes #223

The current behavior is unchanged. The new default will be "recent", since the last 100 beats doesn't really correspond to a specific time period. Currently available options are 3h, 6h, 24h, 1w. Since these are manually triggered when the user selects, I don't think performance will be a big concern.

Slight issue: Updating the period will cause the heartbeat bar animation to trigger, since the data structure is shared. I don't see any easy solution to this.

In the future we can make the default period configurable, but should the Chart component handle this? Or should the LIMIT 100 be configurable?

[chakflying]

New method of storing data implemented. Feels like magic to me but apparently custom watchers is a thing.

[louislam]

Great demanding feature.
I tweaked a little bit, the loading transition should be a bit better when switching to 1w.

[chakflying]

Thanks! Was thinking if I need to write unit test for the API, but I guess we haven't set that up yet.

[louislam]

Thanks! Was thinking if I need to write unit test for the API, but I guess we haven't set that up yet.

I think this pull request do not require unit testing, as it is pretty straight forward.

Only large charges like #518 and #752 need to come with unit tests.

I updated the contributing guide recently:
https://github.com/louislam/uptime-kuma/blob/master/CONTRIBUTING.md#-low-priority---harsh-mode

[Zixim]

Could this setting be sticky?
i.e. If a chart is set to 1w, keep it set to 1w.
Now, it reverts to Recent when navigating away & returning to the chart.

[derekoharrow]

Could this setting be sticky? i.e. If a chart is set to 1w, keep it set to 1w. Now, it reverts to Recent when navigating away & returning to the chart.

Yes please - this would be great. That and perhaps adding a "default" setting to the Settings - e.g. so we can default all items to say 24 hours.

[chakflying]

PR for saving the period is open, please discuss in #1007.