Kubectl does not support secret creation from `.env` files with multiline values

### What happened?

`kubectl` currently does not support the creation of Kubernetes secrets from .env files containing multiline values. This limitation poses a challenge for users who need to store multiline environment variables as secrets, such as certificates or private keys.

Assuming the following `.env` file:
```.env
SECRET_ONE_LINE=Value one line

PASSPORT_PRIVATE_KEY="-----BEGIN RSA PRIVATE KEY-----
MIIEpAIBAAKCAQEAx+4sI6wK3b7q2C4RjN02pH/sy9vwZ9Xbb1hjQmQY/V2aG5QQ
... (rest of the private key) ...
-----END RSA PRIVATE KEY-----"

PASSPORT_PUBLIC_KEY="-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAx+4sI6wK3b7q2C4RjN02
... (rest of the public key) ...
-----END PUBLIC KEY-----"

```

And running `kubectl create secret generic test-secret --from-env-file=.env` the following output is given by kubectl:
```sh
error: "MIIEpAIBAAKCAQEAx+4sI6wK3b7q2C4RjN02pH/sy9vwZ9Xbb1hjQmQY/V2aG5QQ" is not a valid key name: a valid environment variable name must consist of alphabetic characters, digits, '_', '-', or '.', and must not start with a digit (e.g. 'my.env-name', or 'MY_ENV.NAME', or 'MyEnvName1', regex used for validation is '[-._a-zA-Z][-._a-zA-Z0-9]*')
```

### What did you expect to happen?

The secret should be created successfully with the multiline value stored.

### How can we reproduce it (as minimally and precisely as possible)?

1. Create a `.env` file with multiline values:
```.env
SECRET=Value
MULTILINE_SECRET="line1
line2
line3"
```
2. Create a Generic Secret:
```sh
kubectl create secret generic test-secret --from-env-file=.env
```

### Anything else we need to know?

_No response_

### Kubernetes version

```console
$ kubectl version
Client Version: v1.29.2
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.28.9+rke2r1
```

### Cloud provider

### OS version

```console
# On MacOs:
$ uname -a
Darwin 200.225.2.32-clientes-izzi.mx 23.4.0 Darwin Kernel Version 23.4.0: Wed Feb 21 21:44:06 PST 2024; root:xnu-10063.101.15~2/RELEASE_ARM64_T8103 arm64

```

### Install tools

### Container runtime (CRI) and version (if applicable)

### Related plugins (CNI, CSI, ...) and versions (if applicable)