feat(mdx): Open absolute links in new tab

[tuhuynh27]

[Link](https://memos.pub/)

Current: Links in markdown files open in the same tab. Expected: I think it's better if links in markdown files default to open in a new tab.

[thien-do]

oh that's right, sorry, will look into this

it uses unifiedjs under the hood btw (rehype remark) so maybe there's a related plugin or we can use one of the current plugin (there's one that rewrite relative links, guess it can also be used for this)

[thien-do]

I think this is quite simple and could be a good first issue! We already have logic to alter the links in markdown files, so all we need is focus on this line:

https://github.com/thien-do/memos.pub/blob/0be2f222f1a51eb843c1ef68fc21fe41d8109f8c/lib/mdx/plugins/url.ts#L32

and instead of doing nothing (return), we should add the "target" attribute to the current node.

Two notes:

• Should have the necessary attributes to prevent attacks (ref/rel)
• Should apply for absolute links only