Python: Renames SK prefix to Kernel (#4716)

### Motivation and Context
The .NET SDK uses the `Kernel` prefix instead of `SK` for the context,
function, model, etc. classes. This PR aligns the Python package with
that policy.

Fixes #4561 
### Contribution Checklist

- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄

python/DEV_SETUP.md

@@ -170,7 +170,7 @@ from this field is sufficient to have these types of classes as valid Pydantic f
 any class using them as attributes to be serialized.
 
 ```python
-from semantic_kernel.sk_pydantic import PydanticField
+from semantic_kernel.kernel_pydantic import PydanticField
 
 class B(PydanticField): ... # correct, B is still an ABC because PydanticField subclasses ABC
 class B(PydanticField, ABC): ... # Also correct
@@ -223,13 +223,13 @@ class A:
         self.d = d
 ```
 
-You would convert this to a Pydantic class by subclassing from the `SKBaseModel` class.
+You would convert this to a Pydantic class by subclassing from the `KernelBaseModel` class.
 
 ```python
 from pydantic import Field
-from semantic_kernel.sk_pydantic import SKBaseModel
+from semantic_kernel.kernel_pydantic import KernelBaseModel
 
-class A(SKBaseModel):
+class A(KernelBaseModel):
     # The notation for the fields is similar to dataclasses.
     a: int
     b: float
@@ -255,14 +255,14 @@ class A:
         self.c = c
 ```
 
-You can uses the `SKGenericModel` to convert these to pydantic serializable classes.
+You can use the `KernelBaseModel` to convert these to pydantic serializable classes.
 
 ```python
 from typing import Generic
 
-from semantic_kernel.sk_pydantic import SKGenericModel
+from semantic_kernel.kernel_pydantic import KernelBaseModel
 
-class A(SKGenericModel, Generic[T1, T2]):
+class A(KernelBaseModel, Generic[T1, T2]):
     # T1 and T2 must be specified in the Generic argument otherwise, pydantic will
     # NOT be able to serialize this class
     a: int