Dekaf runtime changes

[jshearer]

Description:

Rolls up a couple more changes to the agent and runtime for Dekaf:

• Detect tasks intended for Dekaf inside Runtime::unary_materialize() and route them to dekaf::connector::unary_materialize(). Doing it here instead of in build allows more of Flow to interact with Dekaf tasks correctly:
  • The field selection UI uses a dry_run publication (i.e a validate call) to fetch which fields to show. This now intercepts that call and correctly passes it to Dekaf because we set connector_type based on the endpoint in walk_materialization():

    flow/crates/validation/src/materialization.rs

    Lines 126 to 128 in 44dc0db

    	models::MaterializationEndpoint::Dekaf(config) => (
    	flow::materialization_spec::ConnectorType::Dekaf as i32,
    	serde_json::to_string(config).unwrap(),

  • The connector_tags agent task calls a connector's Spec RPC, and we need to get Dekaf's endpoint/resource config schemas somehow so I figured rather than writing a thing to do it manually, all we need to do is send connector_type: ConnectorType::Dekaf when we detect a task with image_name starting in ghcr.io/estuary/dekaf-.
• I also had to skip image pulling in connector_tags when processing a Dekaf row as obviously there's no image to pull.

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