Support cluster-level setting for components

[aylei]

Feature Request

Formerly, we rely on template tools like helm to coordinate fields and eliminate copy-paste redundancy. Now that we are going to migrate the logic of helm to server-side #1121 , TidbCluster should support cluster-level setting for components. Of course, each component could still specify the properties and override the cluster one.

Proposal

Adding the following fields in TidbClusterSpec:

type TidbClusterSpec struct {

+	// Time zone of TiDB cluster Pods
+	Timezone string `json:"timezone,omitempty"`
+	// ImagePullPolicy of TiDB cluster Pods
+	ImagePullPolicy corev1.PullPolicy `json:"imagePullPolicy,omitempty"`
+	// Whether Hostnetwork is enabled for TiDB cluster Pods
+	HostNetwork *bool `json:"hostNetwork,omitempty"`
+	// Affinity of TiDB cluster Pods
+	Affinity *corev1.Affinity `json:"affinity,omitempty"`
+	// PriorityClassName of TiDB cluster Pods
+	PriorityClassName string `json:"priorityClassName,omitempty"`
+	// Base node selectors of TiDB cluster Pods, components may add or override selectors upon this respectively
+	NodeSelector map[string]string `json:"nodeSelector,omitempty"`
+	// Base annotations of TiDB cluster Pods, components may add or override selectors upon this respectively
+	Annotations map[string]string `json:"annotations,omitempty"`
+	// Base tolerations of TiDB cluster Pods, components may add more tolreations upon this respectively
+	Tolerations []corev1.Toleration `json:"tolerations,omitempty"`
}

[aylei]

cc @tennix @weekface @cofyc