Fix template initialization from current working directory (#976)

## Changes
If args[0] == "." was provided to bundle init command, it would try to
resolve it as a built in template and error out.

## Tests
Manually

before:
```
shreyas.goenka@THW32HFW6T mlops-stack % cli bundle init .
Error: open /var/folders/lg/njll3hjx7pjcgxs6n7b290bw0000gp/T/templates3934264356/templates/databricks_template_schema.json: no such file or directory
```

after:
```
shreyas.goenka@THW32HFW6T mlops-stack % cli bundle init .
Welcome to MLOps Stacks. For detailed information on project generation, see the README at https://github.com/databricks/mlops-stacks/blob/main/README.md.

Project Name [my-mlops-project]: ^C
```

libs/template/materialize.go

@@ -104,6 +104,12 @@ func Materialize(ctx context.Context, configFilePath, templateRoot, outputDir st
 
 // If the given templateRoot matches
 func prepareBuiltinTemplates(templateRoot string, tempDir string) (string, error) {
+	// Check that `templateRoot` is a clean basename, i.e. `some_path` and not `./some_path` or "."
+	// Return early if that's not the case.
+	if templateRoot == "." || path.Base(templateRoot) != templateRoot {
+		return templateRoot, nil
+	}
+
 	_, err := fs.Stat(builtinTemplates, path.Join("templates", templateRoot))
 	if err != nil {
 		// The given path doesn't appear to be using out built-in templates

libs/template/renderer_test.go

@@ -86,6 +86,18 @@ func assertBuiltinTemplateValid(t *testing.T, settings map[string]any, target st
 	}
 }
 
+func TestPrepareBuiltInTemplatesWithRelativePaths(t *testing.T) {
+	// CWD should not be resolved as a built in template
+	dir, err := prepareBuiltinTemplates(".", t.TempDir())
+	assert.NoError(t, err)
+	assert.Equal(t, ".", dir)
+
+	// relative path should not be resolved as a built in template
+	dir, err = prepareBuiltinTemplates("./default-python", t.TempDir())
+	assert.NoError(t, err)
+	assert.Equal(t, "./default-python", dir)
+}
+
 func TestBuiltinTemplateValid(t *testing.T) {
 	// Test option combinations
 	options := []string{"yes", "no"}