Add cluster-wide config to override per-pool include_deferred filed

[msumit]

Value prop: As a centralised platform team, we don't want end users to give control of this field, especially when they are totally unaware of what deferred really means here. For them, pool slots are used to control the load on the downstream systems like Spark and Presto, and it doesn't matter whether that task is deferred or not. So with a cluster level config we'll take control of the behaviour.

Changes: Introduced a new configuration option core.pool_include_deferred. When set to True or False, it fixes the effective value for every pool (including pre-existing pools) and prevents users from setting a conflicting per-pool value via the UI, API, or CLI.

The default remains unset (empty string ""), preserving the existing per-pool behavior.

Updated the pool model, local/FastAPI API serializers, UI config endpoint and pool form, CLI pool commands, default pool creation, and added corresponding tests.

• When config is set to True

• When config is set to False

• When someone tries to set an opposite value via API

• When API doesn't contain any info regarding to this flag

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Was generative AI tooling used to co-author this PR?

• Yes - Generated by Claude

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