ENV key validation rules to strict

### Which component(s) is affected?

Kubero UI

### Describe the bug

Hi, the validation rules for environment variable keys are to strict.
They don't allow hypens: `-`

From the UI:
> Only letters, numbers and underscores allowed. Must start with letter or underscore

But hyphens are often used in environment variables.
For example from the Docker Registry image:

`REGISTRY_HTTP_HEADERS_Access-Control-Allow-Origin='[http://registry-ui.example.com]'`

To set various headers.

It would be great to allow this.

### Steps to reproduce

1. Go to the UI and create a new app
2. Set a environment variable, who's key contains a `-`
3. Validation error and unable to create app
4. Uploading a .env also does not work

### Expected behavior

Allow environment variable keys to contain `-`

### Screenshots

_No response_

### Additional information

_No response_

### Debug information

_No response_

Start by locating the Kubero UI validation for environment-variable keys and the code path that processes uploaded .env files. Confirm where hyphens are rejected, then verify that keys containing `-` can be entered and uploaded without validation errors.

Written by the indexing model from the issue text.