Move Inferrer CRD and TypeDef methods to pkg/model

- Move inferrer methods `GetCRDs`, `removeIgnoredOperations`,
`processNested*`, `ApplyShapeIgnoreRules` and `IsShapeUsedInCRDs` to
`pkg/model/crd_util.go`
- Move inferrer method `GetEnumDefs` to `pkg/model/enum_def.go`
- Move inferrer methods `GetTypeDefs`, `processNestedFieldTypeDefs`,
`replaceSecretAttrGoType` to `pkg/model/type_def_util.go`

Author: a-hilaly