update document and variable description for cloud_armor_tier

### TL;DR

cloud_armor_tier now accepts `CA_ENTERPRISE_ANNUAL`

### Expected behavior

_No response_

### Observed behavior

_No response_

### Terraform Configuration

```hcl
N/A
```

### Terraform Version

```sh
N/A
```

### Terraform Provider Versions

```sh
N/A
```

### Additional information

_No response_