[Security Solution] OpenAPI stringifyZodError generates verbose and confusing error message

[machadoum]

Describe the bug:
The function stringifyZodError which is used by buildRouteValidationWithZod returns verbose and confusing error messages for some OpenAPI schemas.

Current behavior:
Given the schema defined here:

kibana/x-pack/plugins/security_solution/common/api/entity_analytics/common/common.schema.yaml

Line 251 in f2e6834

RiskScoreWeight:

the following test:

kibana/x-pack/plugins/security_solution/common/api/entity_analytics/common/risk_weights.schema.test.ts

Line 57 in f2e6834

it('rejects if neither host nor user weight are specified', () => {

Produces the error meesgae:
'host: Required, user: Required, type: Invalid literal value, expected "risk_category", value: Invalid literal value, expected "category_1", host: Required, and 3 more'

Expected behavior:
The previous implementation (without OpenAPI) used to produce a more readable error message:

[
    'Invalid value "undefined" supplied to "host"',
    'Invalid value "undefined" supplied to "user"',
]

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-detection-rule-management (Team:Detection Rule Management)

[marshallmain]

Can you add the old zod schema implementation here for comparison?

[marshallmain]

Also, using a discriminated union on type for RiskScoreWeight will likely make the error message a lot clearer. We have an example of how to add a discriminant here.