text: Title: ConversationFilter missing new optional field exclude_external_shared_channels
  Body: `slack_sdk.models.blocks.block_elements.ConversationFilter` is missing the new optional field `exclude_external_shared_channels`
  
  Source:
  https://github.com/slackapi/python-slack-sdk/blob/3337a47199e3eb829cca8c9e653ab6a3111d610d/slack_sdk/models/blocks/block_elements.py#L758-L767
  
  Reference:
  https://api.slack.com/reference/block-kit/composition-objects#filter_conversations