runner: add CentOS runner type

New runner type for CentOS 8 and 9.  Copied from RHEL

internal/runner/centos.go

@@ -0,0 +1,23 @@
+package runner
+
+import "fmt"
+
+type CentOS struct {
+	Version uint64
+}
+
+func (c *CentOS) String() string {
+	return fmt.Sprintf("org.osbuild.centos%d", c.Version)
+}
+
+func (c *CentOS) GetBuildPackages() []string {
+	packages := []string{
+		"glibc", // ldconfig
+	}
+	if c.Version >= 8 {
+		packages = append(packages,
+			"systemd", // systemd-tmpfiles and systemd-sysusers
+		)
+	}
+	return packages
+}