chore(Prettier): add settings for prettier plugin

[tguichaoua]

Please describe the changes this PR makes and why it should be merged:
resolve #4753

Move prettier config into .prettierrc file. Allow VS Code prettier plugin to correctly format files.

Status

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[tipakA]

#3900 Probably still applies here

[tguichaoua]

#3900 Probably still applies here

If it's a problem, it's possible to move config into the package.json.

[papaia]

This line should be changed too

discord.js/package.json

Line 125 in e0e2711

"*.ts": "prettier --write --single-quote --print-width 120 --trailing-comma all --end-of-line lf --arrow-parens avoid"

[papaia]

#3900 Probably still applies here

If it's a problem, it's possible to move config into the package.json.

I believe you should move it to the prettier field in package.json for consistency.