### Steps to reproduce

1. Login as an admin

2. Go to Administration > Files > Attachments

3. Try to click into Attachment max size field


### What is the buggy behaviour?

* User can't click but Begin of the deletion isEnd of the deletion no visual indicator that it's the case

* No explanation as of why


### What is the expected behaviour?

* \[open\] Primerse and make the field read-only

* \[open\] Add caption: "You can edit this value via environment variables if you have access."


###

### Screenshots and other files

<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/924785/content">

### Environment information

**OpenProject version**

Core build

[06486d686f171fc5d30e7134bbd2acfe44d4c467](https://qa.openproject-stage.com/external_redirect?url=https%3A%2F%2Fgithub.com%2Fopf%2Fopenproject%2Fcommit%2F06486d686f171fc5d30e7134bbd2acfe44d4c467)

Product version

[0f7af0f462587a6870a9b6d47bd4be6bdbd8ff20](https://qa.openproject-stage.com/external_redirect?url=https%3A%2F%2Fgithub.com%2Fopf%2Fsaas-openproject%2Fcommit%2F0f7af0f462587a6870a9b6d47bd4be6bdbd8ff20)

Core version

OpenProject 17.9.0

**Browser**

* [ ] Chrome
* [x] Firefox
* [ ] Safari
* [ ] Mobile Safari
* [ ] Other (please specify)

**Operating System**

* [x] Windows
* [ ] Mac OS X
* [ ] Mobile iOS
* [ ] Mobile Android
* [ ] Linux (please specify distro)
* [ ] Chrome OS
* [ ] Other (please specify)