Update the resources properties to be compatible with Terraform and OpenAPI generator

[slonka]

Description

This is a mirror of #12790 but for resources (Mesh, MeshGateway, MeshExternalService, MeshService, MeshMultizoneService)

Description

We identified 4 types of properties:

• mergable
• non mergeable, user optional, with default
• non mergeable, user optional, without default
• non mergeable, user required

The full doc: https://docs.google.com/document/d/1ZV8KaXr1kV4P5O-eq4gy5IxSMJQ4VzvTT-BmeBABuDo/edit?tab=t.0

We should modify the properties and have a linter to check that we're not introducing new fields that don't match.

Parent issue: https://github.com/Kong/kong-mesh/issues/7206

For proto we should use google.protobuf.BoolValue skipMTLS = 4; so when user sets this to false then API returns false