* Fix tags field to be shown as array in API view
`tags` field in serializers is defineded as `TagListSerializerField`.
It should be shown as an array value in API view but actually, it is a
simple string value.
This fixes it by introducing a new `FieldInspector` to handle
`TagListSerializerField` type field as an array. It doesn't affects any
other type fields.
* Fix SerializedPKRelatedField type API expression
A field definded as `SerializedPKRelatedField` should be shown as an
array of child serializer objects in a response value definition in API
view but it is shown as an array of primary key values (usually
`integer` type) of a child serializer.
This fixes it by introducing a new `FieldInspector` to handle the field.
It doesn't affect any other type fields.
* Fix request parameter representation in API view
In API view, representation of a parameter defined as a sub class of
`WritableNestedSerializer` should be vary between a request and a
response. For example, `tenant` field in `IPAddressSerializer` should be
shown like following as a request body:
```
tenant: integer ...
```
while it should be shown like following as a response body:
```
tenant: {
id: integer ...,
url: string ...,
name: string ...,
slug: string ...
}
```
But in both cases, it is shown as a response body type expression. This
causes an error at sending an API request with that type value.
It is only an API view issue, API can handle a request if a request
parameter is structured as an expected request body by ignoring the
wrong expression.
This fixes the issue by replacing an implicitly used default auto schema
generator class by its sub class and returning a pseudo serializer with
'Writable' prefix at generating a request body. The reason to introduce
a new generator class is that there is no other point which can
distinguish a request and a response. It is not enough to distinguish
POST, PUT, PATCH methods from GET because former cases may return a JSON
object as a response but it is also represented as same as a request
body, causes another mismatch.
This also fixes `SerializedPKRelatedField` type field representation. It
should be shown as an array of primary keys in a request body.
Fixed#2400
