[Synthetics] Evaluate validation schema for bulk project monitor api

[dominiqueclarke]

Describe the feature:
We do not currently have any route-side kbn-schema defined for the monitor client contract for project monitors. However, we do use io-ts to define the client contract and the monitor SO configured from it are valid.

We should see if there's any opportunity to use kbn-schema for monitor client contract, or if it's best to continue using io-ts exclusively since the monitor types are so complex.

We should also ensure that the client side type currently used by io-ts is strict enough.

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)

[shahzad31]

i don't think it's worth to add kbn-schema validation since we already have io-ts validation