Add fnr validation component

frontend/src/components/fnr/index.tsx

+import { useForm } from 'react-hook-form';
+import validator from '@navikt/fnrvalidator'
+
+const isValidIdnr = (data: string) => {
+    const validationResult = validator.idnr(data)
+    return validationResult.status === "valid"
+}
+
+
+function Fnr() {
+    const { register, handleSubmit, formState: { errors } } = useForm();
+
+    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" />
+        {errors.fnr && errors.fnr.message}
+        {errors.fnr && errors.fnr.type === "validate" && 'Invalid fnr'}
+        <br />
+        <input type="submit" />
+    </form >
+}
+
+export default Fnr