Customize user identification stage input placeholder

**Describe your question**
I would like to adjust the placeholder text that appears in the username box during the default authentication flow. Currently, it says "UPN or Username," which makes sense given how I've configured it. Still, I would prefer it say something like "user@domain.tld." I don't think this can be done with CSS, and I'm not sure how I would go about adding Javascript code to my install to make this work. If there's anything I can somehow adjust to make this happen, I'd appreciate if someone could let me know. Thanks!

**Relevant infos**
I'm running my Authentik instance using Docker with some custom CSS to adjust visual parameters like the background image.

**Screenshots**

**Logs**
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**Version and Deployment (please complete the following information):**

- authentik version: 2023.10.4
- Deployment: docker-compose

**Additional context**
N/A