feat(credential): add credential type to credential library on create

This change adds a credential type attribute to credential library and
allows it to be set when creating a credential library.

Specifying the type of credential returned from a library allows for new
features and additional error checking to be added over time. A
User Password credential type and an Unspecified credential type are
included with the expectation that additional credential types will be
added in the future. This change also adds the credential type attribute
to existing credential libraries and sets it to Unspecified.

Known Limitations:

- Credential type is only supported on the repository create method.
  Support for the other CRUD methods will be added in the future.

internal/errors/code_test.go

@@ -287,6 +287,11 @@ func TestCode_Both_String_Info(t *testing.T) {
 			c:    VaultEmptySecret,
 			want: VaultEmptySecret,
 		},
+		{
+			name: "VaultInvalidMappingOverride",
+			c:    VaultInvalidMappingOverride,
+			want: VaultInvalidMappingOverride,
+		},
 		{
 			name: "OidcProviderCallbackError",
 			c:    OidcProviderCallbackError,