Added support for button properties.

Description

Fixes #416

Added support for the new button property added to Notion. (ButtonProperty,ButtonPropertyValue) This fixes a problem that caused an exception when deserializing a query.

The button property information is shown below in JSON, and it appears that the button field is returned as an empty object at this time, even if the button property settings have been customized in Notion. Therefore, the object that receives the button field is implemented as an empty class.

DB property "testBtn":{ "id":"_ri%7C","name":"testBtn","type":"button","button":{ } },

Page property "testBtn":{ "id":"_ri%7C","type":"button","button":{ } },

The existing test code has been modified to support the button property.

Type of change

[x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

The unit test completed successfully and I tested with my Notion integration that the page and database queries and the search API work properly.

Checklist:

[x] My code follows the style guidelines of this project
[x] I have performed a self-review of my own code
[x] I have commented my code, particularly in hard-to-understand areas
[ ] I have made corresponding changes to the documentation
[x] My changes generate no new warnings
[x] I have added tests that prove my fix is effective or that my feature works
[x] New and existing unit tests pass locally with my changes
[x] Any dependent changes have been merged and published in downstream modules
[x] I have checked my code and corrected any misspellings

notion-dotnet / notion-sdk-net