Add fnr validation component

frontend/src/components/form/fnr.tsx

-import { useForm } from 'react-hook-form';
+import React from 'react'
 import validator from '@navikt/fnrvalidator'
+import { UseFormReturn } from "react-hook-form";
 
-const isValidIdnr = (data: string) => {
+export function isValidIdnr(data: string) {
     const validationResult = validator.idnr(data)
     return validationResult.status === "valid"
 }
 
+interface FnrProps
+    extends Partial<Pick<UseFormReturn, "register">> {
+    name: string
+    label?: string
+    errors?: any
+}
 
-function Fnr() {
-    const { register, handleSubmit, formState: { errors } } = useForm();
+export default function Fnr(props: FnrProps) {
+    const { register, name, errors, ...rest } = props
+    if (register === undefined) {
+        return <></>
+    }
 
-    return <form onSubmit={handleSubmit((data) => { console.log(data) })}>
-        <label htmlFor="fnr">Fnr: </label>
-        <input type="text" placeholder="fnr" {...register("fnr", { required: "Fnr is required", validate: isValidIdnr })} id="fnr" />
+    return <>
+        <input type="text" placeholder="fnr" {...register(name, { required: "Fnr is required", validate: isValidIdnr })} id="fnr" />
         {errors.fnr && errors.fnr.message}
         {errors.fnr && errors.fnr.type === "validate" && 'Invalid fnr'}
-        <br />
-        <input type="submit" />
-    </form >
+    </>
+
 }
 
-export default Fnr