Update file doorkeeper.en.yml - add scope `admin_mode`

What does this MR do and why?

This MR intends to add the newly introduced scope admin_mode to the doorkeeper file.

Screenshots or screen recordings

N/A

How to set up and validate locally

https://docs.gitlab.com/ee/api/oauth2.html#retrieve-the-token-information

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.