[Actionable Observability] - {{context.alertDetailsUrl}} for Infra Inventory and Metric Threshold rule types

[fkanout]

📝 Summary

Part of #138645

We need to provide the link to the Alert Details page for a given alert as an Action Variable.

Here is an example PR for a similar task.

✅ AC

• Alert Details URL {{context.alertDetailsUrl}} should appear as one of the rule variables when defining the rule action.
• The correct URL a given alert should appear when viewing the alert notification in its final destination (for example: when the recipient views the email containing the alert e.g. /eyg/app/observability/alerts/9f41dd88-3028-4196-a6c8-279f649ffc86

[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)

[fkanout]

@vinaychandrasekhar @maciejforcone, Action variables require description, would you please provide one for {{context.alertDetailsUrl}}. Thanks!

[CoenWarmer]

Just discussed with @vinaychandrasekhar on Slack. Agreed @maciejforcone should be in this discussion as well.

[vinaychandrasekhar]

For the "View In App" URL/link, we currently offer the following description - "Link to the view or feature within Elastic that can be used to investigate the alert and its context further".
I think we should change that to something like "Link to the view or feature within Elastic that can assist with further investigation".
And for the alert details URL, we can offer something like "Link to the view within Elastic that shows further details and context surrounding this alert"

@maciejforcone your thoughts appreciated. My guidance is to keep the wording consistent, yet distinguish between what those two links offer users.