Update serverless roles API tests

[jeramysoucy]

The serverless API tests are all in process of being updated to use non-operator authentication. The roles APIs should be updated to use an appropriate access level role, and to manipulate non-reserved roles (these currently target the superuser role and will return 400's and 401's instead of the expected status).

e.g. file https://github.com/elastic/kibana/blob/main/x-pack/test_serverless/api_integration/test_suites/common/platform_security/roles_routes_feature_flag.ts

In serverless the roles APIs are gated behind feature flags, which need to be enabled in the corresponding feature flag configs.
e.g file x-pack/test_serverless/api_integration/test_suites/observability/config.feature_flags.ts
Required ES flag: xpack.security.authc.native_roles.enabled=true

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)

[legrego]

@jeramysoucy to check if this has been resolved.