sam deploy doesn't fail when it can't find the config / template file

### Description:

When using `--config-file` and `--template-file` with `sam deploy`, the files weren't being used

### Steps to reproduce:

Set up a project structure like so:

```
~/ExampleProject/Makefile
~/ExampleProject/deployment/samconfig.toml
~/ExampleProject/project/template.yaml
```

From `ExampleProject/` run the following:

```
sam deploy \
--config-env=example \
--config-file="./deployment/samconfig.toml" \
--template-file="./project/template.yaml"
```

### Observed result:

```
Usage: sam deploy [OPTIONS]
Try 'sam deploy -h' for help.

Error: Missing option '--stack-name', 'sam deploy --guided' can be used to provide and save needed parameters for future deploys.
```

### Expected result:

Either return an error that `./deployment/samconfig.toml` and `./project/template.yaml` could not be accessed/found OR find the file from the current working directory.

The desired result can be found with an absolute path to the files.

### Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: Fedora 34
2. `sam --version`: SAM CLI, version 1.33.0
3. AWS region: us-west-1