Feat: Full server-side pagination for important events

[chakflying]

⚠️⚠️⚠️ Since we do not accept all types of pull requests and do not want to waste your time. Please be sure that you have read pull request rules:
https://github.com/louislam/uptime-kuma/blob/master/CONTRIBUTING.md#can-i-create-a-pull-request-for-uptime-kuma

Tick the checkbox if you understand [x]:

• I have read and understand the pull request rules.

Description

• Remove the use of sendImportantHeartbeatList
• There is no longer a global state of importantHeartbeatList in vue
• Implement server-side pagination, where on initial load, the view request the total number of items, then each page of items is only loaded as they are selected
• Use a global event bus mitt to pass new important heartbeats to any list currently active

The code change is relatively simple, but the performance improvement should be significant.

Fixes #726
Fixes #758
Fixes #3497
Fixes #3494
Fixes #3127
Fixes #1716
Fixes #1397
Fixes #2346

Type of change

• Performance optimization

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas
  (including JSDoc for methods)
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)

[CommanderStorm]

Overall, very clean. I have left some minor inline comments.

One question:
Why did you add mitt exactly? (instead of function calls)

[CommanderStorm]

Is the reactivity in this case correct? (am I missing something?) 🤔

Let's assume that monitor=null ⇒ the code is skipped.
If I then monitor gets populated ⇒ getImportantHeartbeatListPaged is never called or am I missing something?

[chakflying]

Good point. This code normally works because AFAIK in the vue lifecycle computed runs before mounted, so this.monitor should be true. I added a watch for monitor in case the monitorList has not been loaded when we are mounted for some reason.

[chakflying]

we need to send an event from the root of the vue app to deep inside the component tree Details.vue. I'm not aware of any function calls that can do this.

I looked through the alternatives suggested in the Vue 3 Docs but none of them seemed helpful, so the global event bus option was chosen.

[CommanderStorm]

I found this issue, which is likely fixed by this PR:
#758

[Saibamen]

Could this be ported to 1.23.x branch?

[CommanderStorm]

Given how many performance improvements have gone into v2, I would argue that migrating to v2 would be a better choice for our userbase.

=> I think classifying speed as a feature instead of a bug is very reasonable