Add admin endpoints for downloading/uploading files

[eleftherioszisis]

Description

Add endpoints for downloading and uploading files using the admin routes

Acceptance criteria

• Download file as admin
• Upload file as admin

[evakennyobi]

Can be closed @eleftherioszisis ? thanks

[eleftherioszisis]

Not yet. I have implemented only the downloading part. Will do the uploading part too shortly.

[eleftherioszisis]

Changes have been deployed to staging with entitycore 2026.5.6. entitysdk client changes available for entitysdk>=v0.17.0