… in integration tests (elastic#227689)

**Resolves: elastic#220333
**Resolves: elastic#227571
**Resolves: elastic#219407

## Summary

This PR fixes flakiness caused by the real prebuilt rules package installation.

## Details

Multiple Rule Management API endpoints install the prebuilt rules package under the hood when it's not installed. In normal case this installation happens from the EPR. The problem is that EPR might be unavailable for some period of time or there network issues blocking EPR access. On top of that real package is heavy and requires some time and resources to be installed. While the major part of our functionality doesn't depend on the real prebuilt rules package and the concrete rules there. On top of that API endpoints depending on the real prebuilt rules package fail with HTTP 500 error when EPR is unavailable.

This PR extends the Functional Test Runner with `rootHooks.beforeAll` configuration option which is used to install a lightweight mock prebuilt rules package. This action prevents real package installation make the tests much more predictable.

## Flaky test runner

- ✅ [ECH import custom rules integration tests (200 runs)](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/8627)
- ✅ [Serverless import custom rules integration tests (200 runs)](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/8642)

(cherry picked from commit 76908c5)