[BUG] Impossible to create/update detector when one data source index is closed

[lsoumille]

What is the bug?
It's impossible to create or update a detector when one index behind the alias data source is closed

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Edit an existing detector
2. Pick an alias as data source with a closed index
3. Save your changes

What is the expected behavior?
We would expect to update to be able to create or update a detector even though all the index behind the data source are not opened. In our case we are closing indexing older than 1 month to keep a good search performance. We keep them for some time in case of an incident.

What is your host/environment?

• OS: WS2022
• Version 2.15
• Plugins

Do you have any screenshots?

Do you have any additional context?
I tried to open all the old indexes we have in the cluster and it solved the issue. However the detector is able to detect newly suspicious behaviours

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