Docusaurus upgrade CLI command

[slorber]

🚀 Feature

It would be convenient to have a yarn docusaurus upgrade command.

It would just bump the @docusaurus version numbers and run docusaurus clear to ensure caching does not cause any trouble (like #4070)

It's complicated to automate the update of breaking changes so it wouldn't be an initial goal of this CLI (but maybe we can improve it later)

[semoal]

Worked on a solution to this.
Accepts a --tag option to pass custom npm tags (alpha, beta, next, latest.. any)

Preview of docusaurus upgrade -t alpha:

Preview of docusaurus upgrade:

It automatically detects if you're using yarn or npm, to use npm install x@tag or yarn upgrade x@tag.

Probably this should be enough, if you're ok with this i can open a pr later