Fix manifest validation for random-route

[tcdowney]

The validator was always raising the following error when random-route was specified:
"default-route and random-route may not be used together"

This change makes it so that it only errors when both default-route and random-route are set to true.

Related Slack discussion: https://cloudfoundry.slack.com/archives/C0297673ASK/p1687556306576749

Is there a related GitHub Issue?

No

What is this change about?

Fixes a bug where any manifest containing random-route: true would cause an error. Minimal example:

--- 
applications: 
- name: dora
  random-route: true

15:57 $ cf push node
Pushing app node to org o / space s as cf-admin...
Applying manifest file /Users/tdowney/go/src/github.com/cloudfoundry/cf-acceptance-tests/assets/node/manifest.yml...

Updating with these attributes...
  applications:
  - name: node
    random-route: true
applications[0].default-route and random-route may not be used together

Does this PR introduce a breaking change?

No

Acceptance Steps

Push an app with manifests containing random-route, default-route, and mixtures of both. They should work in isolation and fail when both are set to true.

Tag your pair, your PM, and/or team

@acosta11

[acosta11]

Looks good. See the related korifi-dev slack thread for other equivalent options for the validation code. If other folks have a strong preference we can update afterwards.