User can add restricted roles while adding/removing roles from dashboard site

Issue Description

Users can add any role by modifying the payload while adding groups from the dashboard site.

Expected Behavior

Users should only have the authority to add roles that exist in the database.

Current Behavior

By modifying the payload user can choose any role of their choice. And then it will get applied to them on discord.

Screenshots

Reproducibility

• This issue is reproducible
• This issue is not reproducible

Steps to Reproduce

1. Modify the API response for adding roles

Severity/Priority

• Critical
• High
• Medium
• Low

Additional Information

Checklist

• I have read and followed the project's code of conduct.
• I have searched for similar issues before creating this one.
• I have provided all the necessary information to understand and reproduce the issue.
• I am willing to contribute to the resolution of this issue.

Start by tracing the dashboard API endpoint used for adding or removing roles and follow where the submitted role is accepted before being applied on Discord. Verify the validation against roles in the database, then reproduce the modified-payload case and confirm unauthorized roles are rejected while valid roles still work.