Add an extra warning when ILM will affect system indices

[marius-dr]

Right now there is no specific warning for ILM policies that will affect system indices. It would be good to have a similar warning to the one from Index Management. ( #39018 )

Case in point where it seems to have affected an user: https://discuss.elastic.co/t/accident-deletion-of-kibana-index-but-visualization-is-still-intact/205766/10

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)

[cjcenizal]

@elastic/es-data-management With the introduction of system and hidden indices, do we still need to worry about ILM accidentally capturing them? It seems like this shouldn't be an issue any more, right?

[jakelandis]

It can still be an issue. The relationship is that an index applies an ILM policy. We know which indices are hidden and/or system indices apply which ILM policies. But that does not preclude other non system/hidden indices from re-using those ILM polices (or those ILM polices from being updated). We introduced a meta field with a managed flag to start to help to differentiate between user ILM policies and system ILM policies. (but not exactly what you are asking about here). If anything with the current approach, I might suggest an additional warning in the UI and encourage users to "Save as new policy" if the existing policy has the managed flag.

cc @andreidan since he is starting to think more strategically how to better separate concerns such as these.

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)