[BUG] Honor configured timeout for scheduled PPL execution

[c0depirate69]

Description

This PR fixes scheduled PPL monitor executions timing out around 60 seconds by explicitly setting transport request timeout when Alerting executes PPL queries on schedule.

The timeout is now derived from the existing setting:
plugins.alerting.ppl_query_max_execution_duration

The change is applied to both scheduled PPL execution paths:

• Base PPL query execution
• Custom trigger PPL query execution

This aligns scheduled execution behavior with expected PPL execution duration instead of relying on transport defaults.

Related Issues

Resolves #2190

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created. Not applicable, no API changes.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

Validation run:

• :alerting:compileKotlin -x test
• :alerting:test --tests "PPL"

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.