[Uptime] Add Uptime notification that ZIP URL monitors will be removed

[paulb-elastic]

As part of deprecating ZIP URLs, we need to start notifying users that this (beta) feature will be going away, with a preference to use Project Monitors instead.

Note that this doesn’t cover the actual deprecation which will be done later than this initial notification (more details in #137508).

ACs: (to be confirmed)

• Add a notification in Uptime to inform users that ZIP URLs will be going away in the near future, and that they should migrate them to Project Monitors
• Ideally this notification should only appear for those Uptime accounts that have at least 1 ZIP URL monitor configured

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)

[hbharding]

I synced with @dominiqueclarke about this earlier. There are two places we identified where we think it makes sense to inform users that Zip URLs will be deprecated:

• On the Synthetics "Add Integration" page where users and can add a Zip URL (to help steer them away from using it for new monitors)
• On Uptime's "Monitors" list page, only if monitors created from a Zip URL exist.

As we think about the UX and what this notification should communicate, users may want to know:

1. Why are ZIP Urls being deprecated? Are they being replaced by something else? (good opportunity to introduce the benefits of Project Monitors)
2. Do I need to do anything? If so, what is the recommended process? (do we have appropriate documentation we can point them to?)
3. How many / which of my monitors are affected? (it may be useful to know which monitors need to be "updated" since we don't indicate anywhere if a monitor was created via Zip URL Without this info, users may not know where to begin)

I recommend using a yellow "warning" callout in the two areas mentioned above. The messaging should be slightly different since they appear in different contexts.

• On the "Add integration" page, we can simply say ~"Deprecated. Recommend using project monitors instead... link to project monitors" below the Zip URL tab. Use a small callout since space is tight on this page.
• On Uptime's Monitor list page, it can be a little more verbose and say: "Deprecated. You have existing monitors that will be affected in the future... Project Monitors (which offer X benefit(s) are the new way ... here is what you need to do... link to docs... link to project monitors.... link to see list of affected monitors (show list in a modal)". This can appear at the top of the page, directly below the "Monitors" page header. Users may also want to be able to dismiss (= hide) this message. If we do this, we'll need to consider if the message can reappear on a later session (idea from @dominiqueclarke)

I'll be on PTO until the 26th and won't have time to mock this up before I leave. I suggest working with @colleenmcginnis or @florent-leborgne on any copy suggestions or reviews while I'm out.