Update v2 endpoint to not have as many validation options

[kristinapathak]

Validation configuration will apply completely in v3. v2 already has a fix to warn when TTL Validation doesn't pass and then default to the max TTL. For URL validation, v2 will only enforce loopback validation (if configured).

Example configuration:

    validation:
      url:
        httpsOnly: true
        allowLoopback: false
        allowIP: false
        allowSpecialUseHosts: false
        allowSpecialUseIPs: false
        invalidHosts: []
        invalidSubnets: []
      ttl:
        max: 1m
        jitter: 1s