[Uptime] Alerting - Copy Uptime alert state to context

[dominiqueclarke]

Relates to: #126280

Uptime alerts currently prefer state over context. Many helpful variables for users to craft alert connectors are managed on state, rather than context.

State variables are serialized and persisted in the task manager document. They are primarily intended to persist data across one alert execution to another. However, Uptime does not actually use any of the values in state across alert executions. If we do not need to have access to this data across executions, we should prefer context.

In addition, alerting will now offer rules the ability to specify context variables for recovered alerts, but does not plan to offer the ability to specify state variables for recovered alerts. Moving to context variables where possible will make it easier for us to specify variables in recovered alert messages.

To preserve backward compatibility, Uptime should copy over state variables to context and prefer context in default alert messages.

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)

[awahab07]

Post FF Testing

• context variables are substituted correctly for both Monitor status and TLS alerts.
• state variables work as expected for both Monitor status and TLS alerts.

Rule Type	Template	Message
Monitor status	Monitor {{context.monitorName}} with url {{{context.monitorUrl}}} from {{context.observerLocation}} {{{context.statusMessage}}} The latest error message is {{{context.latestErrorMessage}}}	Monitor Fleet_Server_Health_ext with url https://fleet.34.132.15.251.ip.es.io/api/status from Unnamed-location failed 271 times in the last 15 mins. Alert when > 5. The 30 days availability is 0.00%. Alert when < 99%. The latest error message is received status code 404 expecting [200];;
	Monitor {{state.monitorName}} with url {{{state.monitorUrl}}} from {{state.observerLocation}} {{{state.statusMessage}}} The latest error message is {{{state.latestErrorMessage}}}	Monitor Fleet_Server_Health_ext with url https://fleet.34.132.15.251.ip.es.io/api/status from Unnamed-location failed 271 times in the last 15 mins. Alert when > 5. The 30 days availability is 0.00%. Alert when < 99%. The latest error message is received status code 404 expecting [200]
TLS	Detected TLS certificate {{context.commonName}} from issuer {{context.issuer}} is {{context.status}}. Certificate {{context.summary}}	Detected TLS certificate fleet.34.132.15.251.ip.es.io from issuer R3 is expiring. Certificate expires on Jul 8, 2022 in 29 days.;;
	Detected TLS certificate {{state.commonName}} from issuer {{state.issuer}} is {{state.status}}. Certificate {{state.summary}}	Detected TLS certificate fleet.34.132.15.251.ip.es.io from issuer R3 is expiring. Certificate expires on Jul 8, 2022 in 29 days.