Deploy KServe in Serverless mode by default

[phoevos]

Currently, we set RawDeployment as the default mode for the kserve-controller charm:

kserve-operators/charms/kserve-controller/config.yaml

Lines 4 to 7 in fa49413

	deployment-mode:
	default: "RawDeployment"
	description: Deployment mode for kserve. It can only be RawDeployment or Serverless, and the latter requires knative-serving to be present in the model, and the local-gateway relation to be established.
	type: string

However, this is not working as expected at the moment:

• Unreachable URLs in status of RawDeployment InferenceService #148

Goal

Replace RawDeployment with Serverless as the default deployment mode.