Add nodeSelector, tolerations and imagePullSecrets for the EPP under spec.advanced.inferencePool

Problem

InferencePoolAdvancedSpec (operator/api/v1alpha1/llmmodel_types.go) exposes only schedulerConfig. nodeSelector, affinity and tolerations exist only under spec.advanced.vllm and apply to the model pod. There is no way to place the EPP Deployment or give it imagePullSecrets.

Customer report: a two-node cluster (one GPU node, one CPU node) where the EPP image became unpullable (https://github.com/Concepts-NREC/Nebari-GitOps, see the llm-serving-pack default-image issue). One EPP replica ran on the GPU node with the image already present; the other sat in ImagePullBackOff on the CPU node. They could not pin the EPP to the node that had the image, and hand-patching the EPP Deployment was reverted by the operator within ~90s.

Proposal

Add to InferencePoolAdvancedSpec:

NodeSelector     map[string]string             `json:"nodeSelector,omitempty"`
Tolerations      []corev1.Toleration           `json:"tolerations,omitempty"`
Affinity         *corev1.Affinity              `json:"affinity,omitempty"`
ImagePullSecrets []corev1.LocalObjectReference `json:"imagePullSecrets,omitempty"`
Replicas         *int32                        `json:"replicas,omitempty"`

and thread them through buildEPPDeployment in reconcilers/inferencepool.go. Replicas is included because a single-node or two-node cluster has no reason to run two EPPs; today the count is hardcoded.

Also consider an operator-level default (defaults.epp.imagePullSecrets, defaults.epp.nodeSelector) alongside defaults.epp.image, since a private mirror is a cluster-wide decision rather than a per-model one.

Start with InferencePoolAdvancedSpec in operator/api/v1alpha1/llmmodel_types.go and the buildEPPDeployment function in reconcilers/inferencepool.go. Trace how schedulerConfig reaches the EPP Deployment, then thread the proposed scheduling, pull-secret, and replica fields through the same path. Done means the EPP Deployment reflects these spec settings and operator reconciliation preserves them.