[Uptime] Implement “no data” check to drive the “no data screens” for Uptime

[paulb-elastic]

This PR will add new “no data” screens across the various Observability apps, however this relies on each solution implementing a check that there is no data, which is that this issue is covering.

ACs:

• Implement a check as described in [Observability] New "No Data" screens #107709 that identifies when data has ever been ingested into Uptime

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)

[shahzad31]

Uptime already has an API to do that check. index_status api returns doc count and index exists flags.
Which can be used to differentiate between having no data in current date range and not having any indexes.

[dominiqueclarke]

@shahzad31 @paulb-elastic

No data state LGTM.

However, at times there is a flash of loading content, including the monitors heading and date picker. It doesn't seem as noticeable as UX was before we resolved that issue, but does appear sometimes. I've added #115960, but @paulb-elastic can you help me determine if this is needs to be fixed for 7.16?

[paulb-elastic]

However, at times there is a flash of loading content, including the monitors heading and date picker. It doesn't seem as noticeable as UX was before we resolved that issue, but does appear sometimes. I've added #115960, but @paulb-elastic can you help me determine if this is needs to be fixed for 7.16?

I've commented in #115960 (comment)