feat(web-api): add authorship arguments to assistant threads and chat stream

[zimeg]

Summary

This PR adds the "authorship" arguments - icon_emoji, icon_url, and username - to the following methods:

• assistant.threads.setStatus
• chat.startStream

Reviewers

Please feel free to experiment with the following code example:

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

await client.assistant.threads.setStatus({
  channel_id: "C018QLSQ38A",
  thread_ts: "1765934795.222209",
  status: "dancing...",
  username: "Charlie Brown",
  icon_emoji: "maple_leaf",
});

await sleep(4000);

const response = await client.chat.startStream({
  channel: "C018QLSQ38A",
  thread_ts: "1765934795.222209",
  recipient_team_id: "T07L2FPUY",
  recipient_user_id: "U0187GKV2US",
  username: "Charlie Brown",
  icon_emoji: "maple_leaf",
});

await sleep(2000);

await client.chat.appendStream({
  channel: "C018QLSQ38A",
  ts: response.ts,
  markdown_text: "Dancing with snoopy dog.",
});

await sleep(2000);

await client.chat.stopStream({
  channel: "C018QLSQ38A",
  ts: response.ts,
});

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.09%. Comparing base (bb284c6) to head (01a7c92).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2455   +/-   ##
=======================================
  Coverage   93.09%   93.09%           
=======================================
  Files          40       40           
  Lines       11240    11240           
  Branches      713      713           
=======================================
  Hits        10464    10464           
  Misses        764      764           
  Partials       12       12           

Flag	Coverage Δ
cli-hooks	95.23% <ø> (ø)
cli-test	94.79% <ø> (ø)
oauth	77.39% <ø> (ø)
socket-mode	61.87% <ø> (ø)
web-api	98.11% <ø> (ø)
webhook	96.66% <ø> (ø)

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[zimeg]

🏷️ note: Marking this as draft while server side changes are being made!