[openstreetmap/openstreetmap-website] Add revoke endpoint for OAuth2 (Issue #3412)

[Robbendebiene]

### Description

Currently there is no way to [revoke an access token](https://oauth.net/2/token-revocation/). Applications who want to provide a proper logout option rely on such functionality. If they just "throw away" the access token then in theory the token can still be (ab)used.
The standard doorkeeper configuration uses the `/oauth2/revoke` endpoint, but it seems like it is not enabled for openstreetmap?

### Screenshots

_No response_

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