text: Title: Add the method to check equality in Block Kit model classes
  Body: ### Reproducible in:
  
  #### The Slack SDK version
  
  All versions
  
  #### Steps to reproduce:
  
  ```python
  from slack_sdk.models.blocks import DividerBlock
  DividerBlock() == DividerBlock()
  ```
  
  It happens with any pair of equivalent blocks.
  
  ### Expected result:
  
  True
  
  ### Actual result:
  
  False
  
  ### Suggested solution
  
  Implementing `__eq__` in JsonObject.
  
  ```python
  class JsonObject(BaseObject, metaclass=ABCMeta):
      ...
      def __eq__(self, other: Any) -> bool:
          if not isinstance(other, JsonObject):
              return NotImplemented
          return self.to_dict() == other.to_dict()
  ```
  
  This would allow testing user functions that accept and/or return Slack SDK models.