feat: add plugin-replace-assets

[pengzhanbo]

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Provide a description in this PR that addresses what the PR is solving. If this PR is going to solve an existing issue, please reference the issue (e.g. close #123).

What is the purpose of this pull request?

• Bug fix
• New feature
• Other

Description

export default {
  plugin: [replaceAssetsPlugin('https://cdn.com')]
}

source:

![](/images/foo.png)
<img src="/images/foo.png">

dist output:

<img src="https://cdn.com/images/foo.png">
<img src="https://cdn.com/images/foo.png">

[coveralls]

Pull Request Test Coverage Report for Build 15870603923

Details

• 59 of 59 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.2%) to 62.729%

---

Totals
Change from base Build 15753780776:	1.2%
Covered Lines:	1479
Relevant Lines:	2153

---

💛 - Coveralls

[Mister-Hope]

I think you should somehow mention this only works for files located in public folder, and add some ref to vuepress core docs about it.

Starting with / is not clear enough, as I am expecting noob users placing them under src folder directly and ask you why it's not working.

[Mister-Hope]

LGTM except some description in docs.