feat(rest-api-client): add method of plugin.installPlugin

[chihiro-adachi]

Why

• Support plugin.installPlugin method to be able to install an imported plug-in in the Kintone environment.

What

• Add a document for the new method.
• Add new unit tests.

How to test

1. prepare a zip file for a plug-in and upload it in Kintone.
2. run below code and check logs:

import {KintoneRestAPIClient} from '@kintone/rest-api-client';

const client = new KintoneRestAPIClient();

const fileKey = (await client.file.uploadFile({
  file: {
    path: "./files/plugin.zip"
  }
})).fileKey;

if (typeof fileKey == "string") {
  console.log(await client.plugin.installPlugin({fileKey: fileKey}));
}

Checklist

• Read CONTRIBUTING.md
• Updated documentation if it is required.
• Added tests if it is required.
• Passed pnpm lint and pnpm test on the root directory.

[tasshi-me]

LGTMです！！！