[Feature] Missing index file in dayjs/plugin

[lk77]

Describe the bug

Hello,

when importing plugins i should able to do :

import {utc, timezone, localizedFormat} from 'dayjs/plugin';

i does not work because there is no index.js in dayjs/plugin directory

import utc  from './utc';
import timezone  from './timezone';
import localizedFormat from './localizedFormat';
[...]

export {
    utc,
    timezone,
    localizedFormat
    [...]
}

Expected behavior

plugins are importing correclty

Information

• Day.js Version 1.10.4
• OS: Ubuntu
• Browser chrome 89

there is no feature request template so i'm using the bug one.

thanks.