[Security Solution] add feature flag to hide all the attacks/alerts alignment work (elastic#238539)

## Summary

We're about to start working on the attacks and alerts alignment effort
(see [this Epic
ticket](elastic#232341)). All this work
will not be release until late in the `9.3` release cycle.
This PR adds a feature flag so we can safely work without deploying any
changes.

### Checklist

- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

elastic#232574

Author: PhilippeOberti

x-pack/solutions/security/plugins/security_solution/common/experimental_features.ts

@@ -294,6 +294,10 @@ export const allowedExperimentalValues = Object.freeze({
    * Release: 9.2.0
    */
   microsoftDefenderEndpointCancelEnabled: true,
+  /**
+   * Protects all the work related to the attacks and alert alignment effort
+   */
+  attacksAlertAlignment: false,
 });
 
 type ExperimentalConfigKeys = Array<keyof ExperimentalFeatures>;