[ML] AIOps: 8.18 Log Rate Analysis improvements

[peteharverson]

Break out from the full backlog in #187683.
Follow up to #196660.

API

Preview Give feedback

No tasks being tracked yet.

UI

Preview Give feedback

1. If an index doesn't have any keyword type fields, we should indicate that with a proper user facing message and fail the analysis early. At the moment we just have the generic message that says the analysis couldn't identify any statistically significant fields.
2. If the current view returns 0 docs for the time range and date histogram, we should update the empty prompt accordingly and block users from clicking the date histogram to initialize the brushes

Analysis

Preview Give feedback

No tasks being tracked yet.

Text field pattern support

Preview Give feedback

No tasks being tracked yet.

Observability AI Assistant Context

Preview Give feedback

1. "Reset" should reset everything, including the contextual insight. [ML] AIOps: Adds AI Assistant contextual insight to Log Rate Analysis page in ML plugin in Observability serverless #186509 (comment)

Telemetry

Preview Give feedback

No tasks being tracked yet.

Workflows

Preview Give feedback

1. There seems to be an edge case where a link from anomaly detection misses to select the correct spike:

[elasticmachine]

Pinging @elastic/ml-ui (:ml)