Throw error if there is incorrect relatesTo in IDX response

[denysoblohin-okta]

If there is incorrect relatesTo in IDX response from server, it can lead to unexpected behaviour, so throw an error.

In the infinite requests bug scenario remediation select-authenticator-authenticate was falsely selected instead of challenge-authenticator, because canRemediate() returns true due to mistake in line 36:

okta-auth-js/lib/idx/remediators/Base/SelectAuthenticator.ts

Line 36 in 933fff3

.find(({ relatesTo }) => relatesTo.key === authenticator.key);

Phone authenticator has incorrect relatesTo: "$.authenticatorEnrollments.value[9]", so relatesTo.key is undefined and authenticator.key is also undefined, leading to false equality.
Just adding protection against undefined to line 36 fixes infinite loop bug.

Internal ref: https://oktainc.atlassian.net/browse/OKTA-612326