[Detection Engine] Improve index access warning message

[yctercero]

Summary

In response to feedback, we are looking to improve the warning message we show users when they do not have access to all the indices specified by a rule index pattern.

As an example, if a rule has an index pattern of filebeat-* and the user has a role which excludes some indices from filebeat-* we show the following error:

The feedback from users was that this gives the impression that there is something wrong, like maybe no indices were queried within filebeat-*. We discussed doing 2 things:

• Modifying the language to specify that indices were queried, but a subset of the pattern may not have been if the user was not assigned access
• Add a command that the user can run in dev tools, if they would like to understand what indices they have privileges to

[elasticmachine]

Pinging @elastic/security-detection-engine (Team:Detection Engine)

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[yctercero]

@nastasha-solomon @approksiu @ARWNightingale could we get help with figuring out the wording here? What we want to communicate is that we searched all indices to which the user had permissions, but that there may be some indices within the indicated pattern that the user does not have access to and were not searched.