[alerting] [uptime] add {{state.firstTriggeredAt}} timezone support

[jagjag]

Describe the feature:
hi, the alerting message template variant {{state.firstTriggeredAt}} and {{state.lastTriggeredAt}} currently recorded in UTC time zone.
please add a option to convert to local time zone

Describe a specific use case for the feature:
the alerting message triggered time is different from the local timezone which makes people confused about the exact date time the alert generated.

[elasticmachine]

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

[pmuellr]

Thanks for feature request.

We have two related issues already open:

• [alerts] provide mustache functions for ease-of-use in transforming mustache variables #84217 - provide mustache functions for ease-of-use in transforming mustache variables
• [Discuss] Ability to interact with the alert query result - User requests #89161 - ability to interact with the alert query result

The first is a specific implementation request for more mustache helpers, that might be able to help with this.

The second is more general, and I think points to alerting needing to support painless and/or Kibana expressions to transform alert data into action parameters. Presumably, it would be general enough to cover this use case, but there's a lot of design and work to do here.

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)

[mikecote]

Pinging Uptime for awareness seems like something the alerting framework should solve.

[shahzad31]

@mikecote @pmuellr do we also have any plans to add more formatting options like styling bold/color, icons etc to messages? those are especially useful in terms of slack etc

[mikecote]

@shahzad31 this would be done when moving text areas to EUI Markdown, we are tracking the Email one with #66723 but I don't recall issues for others (ex: slack).

[pmuellr]

The templates themselves can include format-specific markup, but there's not a ton you can do formatting-wise w/markdown. bold/italic works for slack and email, but they're different **bold**, __bold__, *italic* , _italic_ for markdown/email, *bold*, _italic_ for slack - the only common one there is italic :-(.

Eventually we should support "Block Kit" for Slack - issue #88832 - not clear how we would present this to users, editing that kind of JSON is the stuff of nightmares. But it's not hard to imagine that you could take a structure like that and also produce some semantically similar HTML, for emails.

[mikecote]

Closing in favour of #84217.