This fixes the migrate to data tiers routing API to take into account
the scenario where the node attribute configuration for an index is more
accurate than the existing `_tier_preference` configuration.
Previously we would simply remove the node attributes routing if there
was a `_tier_preference` configured for the index.
With this commit, we'll look if either the `require.data` or
`include.data` custom routings are colder than the existing `_tier_preference`
configuration (ie. `cold` vs `data_warm,data_hot`) and update the tier
routing accordingly.
eg.
{
index.routing.allocation.require.data: "warm",
index.routing.allocation.include.data: "cold",
index.routing.allocation.include._tier_preference: "data_hot"
}
will be migrated to:
{
index.routing.allocation.include._tier_preference: "data_cold,data_warm,data_hot"
}
This also removes the existing invariant that had the `require.data`
configuration take precedence over a possible `include.data`
configuration, and will now migrate the coldest configuration to the
corresponding `_tier_preference`.
eg.
{
index.routing.allocation.require.data: "warm",
index.routing.allocation.include.data: "cold"
}
will be migrated to:
{
index.routing.allocation.include._tier_preference: "data_cold,data_warm,data_hot"
}
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