feat(v2): add draft feature to blog posts

[lex111]

Motivation

Resolve #2314

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

1. Create a new blog post with approximately the same contents:

---
title: Draft post
draft: true
---

This post is in WIP state and should not be published!

2. Run local development server and make sure the new blog post is displayed.

3. Build website and make sure the new blog post is not in the posts list.

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

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[lex111]

It was necessary to modify the existing tests here and below, so that the tests pass successfully in the CI.

The fact is that in fixtures there is a no date file, it does not have a date, which means that it is calculated from the creation date. But the “oddity” of CI is that it copies, as I suppose this file, and therefore its creation date will always be equal to the current test execution time, which is why expected and received data no longer match!

As I wrote above, this issue applies only to CI, locally tests pass successfully without these changes. But in order to achieve successful execution of tests in CI, we need to exclude the prevItem key from the metadata object since this element will change in the CI environment (CIrcieCI).

I don’t know how clearly I have stated the essence of the problem, but in this case I consider such a solution acceptable, because we ran into details of handling this CI.

[yangshun]

This is awesome, thanks!