fix: add support for streaming messages in enterprise orgs

[mwbrooks]

Type of change

• New feature
• Bug fix
• Documentation

Summary

This pull request adds support for streaming messages in Enterprise Orgs. The current implementation fails to get the team_id when DMs are sent to the bot in an Enterprise Org.

Reviewers

You can test with the following steps:

1. Enterprise Org
   1. Create & install the app on an Enterprise Org (e.g. Developer Sandbox)
   2. Send a DM to the bot & confirm it responds
   3. Invite the bot to a public channel
   4. @Mention the bot and confirm it responds
   5. @Mention the bot in a thread and confirm it responds
2. Standalone Workspace
   1. Create & install the app on an Standalone Workspace
   2. Send a DM to the bot & confirm it responds
   3. Invite the bot to a public channel
   4. @Mention the bot and confirm it responds
   5. @Mention the bot in a thread and confirm it responds

Requirements

• I have ensured the changes I am contributing align with existing patterns and have tested and linted my code
• I've read and agree to the Code of Conduct

[zimeg]

@mwbrooks Fantastic catch! I'm glad these changes match the JS implementation as well:

https://github.com/slack-samples/bolt-js-assistant-template/blob/0a86e79567ed336256b3897b3ed8e2480cf97324/listeners/assistant/message.js#L21-L22

🧪 In testing I found a personal workspace still doesn't have access to the chat.startStream methods but I find a developer sandbox gathers from the context as we hope!