[Alerting] Improve messaging on rule detail page when rule is disabled

[chrisronline]

This came from this PR where we captured an edge case where a rule execution starts and does not finish before the rule is disabled. This now leads to an error scenario for the rule and while testing this change, we noticed that the rule detail page, when the rule is disabled, doesn't show anything and we probably want to change this to show execution history and possibly the last state of the rule execution.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[mikecote]

and possibly the last state of the rule execution

It would be good to make it clear it's the last execution. We previously had the last execution status displayed when the rule was disabled and caused some confusion when it was in error state: #98073 and #87055.

[pmuellr]

I think we should move towards showing all the same info for disabled rules that we do for enabled rules. Historically, we obtained this info from the rule's task state, and we clear that for disabled rules. But we have been moving away from that, and I suspect we can display most/all of the current data we show for enabled connectors. We would want to highlight somewhere in the UX that the rule is disabled, to make sure users can differentiate enabled / disabled state if they end up looking similar (which they don't today).