Update `LinuxMemoryPolicy` requirements

[nayuta723]

Overview

Update LinuxMemoryPolicy requirements

• Change nodes field to be required as per v1.3.0 specification

Runtime Spec Reference

Implemented in runtime-spec as follows:

Found in https://github.com/opencontainers/runtime-spec/blob/main/specs-go/config.go:

LinuxMemoryPolicy

// LinuxMemoryPolicy represents input for the set_mempolicy syscall.
type LinuxMemoryPolicy struct {
	// Mode for the set_mempolicy syscall.
	Mode MemoryPolicyModeType `json:"mode"`

	// Nodes representing the nodemask for the set_mempolicy syscall in comma separated ranges format.
	// Format: "<node0>-<node1>,<node2>,<node3>-<node4>,..."
	Nodes string `json:"nodes"`

	// Flags for the set_mempolicy syscall.
	Flags []MemoryPolicyFlagType `json:"flags,omitempty"`
}

Related to #309