[FEATURE]: Support for newline characters in custom fields

[Petersoj]

⚠️ This issue respects the following points: ⚠️

• This is a feature request for one feature, not a question, discussion or multiple features.
• This is not a feature request for the browser extension or another client.
• This feature is not already requested on Github (I've searched it).
• This feature does not already exist (I checked the wiki).

Current Status

This feature request is similar to #436, but with a different motivation. I ran into one example recently where I was given 2FA backup codes from a website. The backup codes consist of several alphanumeric strings and are newline delimited. Imposing character limits is understandable, but preventing newline characters seems a bit too restrictive, especially when it comes to custom fields. It's generally not too much effort to replace newlines with spaces (which is acceptable in the case of 2FA backup codes), but this would be a nice-to-have feature if it doesn't require too much work or refactoring.

Feature Description

1. Open Passwords app.
2. Create a new password.
3. Add a new custom field with the "secret" or "text" type.
4. Paste in the sensitive string data with newline characters.
5. Sit back and relax, knowing that your custom field data persisted the newline characters.
6. Profit.

Additional Context

No response