feat: add chat.{start|append|stop}Stream api methods

[zimeg]

This PR adds support for the following methods for #1516:

• chat.startStream
• chat.appendStream
• chat.stopStream

Category

• slack-api-client (Slack API Clients)
• slack-api-model (Slack API Data Models)

Reviewers

The following code sample can be used as a working concept:

var result = client.chatStartStream(r -> r
        .token(token)
        .channel(channel)
        .threadTs(ts)
        .recipientUserId(userId)
        .recipientTeamId(teamId));
client.chatAppendStream(r -> r
        .token(token)
        .channel(channel)
        .ts(result.getTs())
        .markdownText("**h"));
client.chatAppendStream(r -> r
        .token(token)
        .channel(channel)
        .ts(result.getTs())
        .markdownText("ello!**"));
client.chatStopStream(r -> r
        .token(token)
        .channel(channel)
        .ts(result.getTs())
        .blocksAsString("[{\"type\":\"context_actions\",\"elements\":[{\"type\":\"feedback_buttons\",\"action_id\":\"feedback\",\"positive_button\":{\"text\":{\"type\":\"plain_text\",\"text\":\"Good Response\" ,\"emoji\":true},\"accessibility_label\":\"Submit positive feedback on this response\",\"value\":\"good-feedback\"},\"negative_button\":{\"text\":{\"type\":\"plain_text\",\"text\":\"Bad Response\",\"emoji\":true},\"accessibility_label\":\"Submit negative feedback on this response\",\"value\":\"bad-feedback\"}}]}]"));

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you agree to those rules.

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.04%. Comparing base (d1f005c) to head (86a0142).

Files with missing lines	Patch %	Lines
...java/com/slack/api/methods/RequestFormBuilder.java	76.66%	4 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1518   +/-   ##
=========================================
  Coverage     73.03%   73.04%           
- Complexity     4381     4398   +17     
=========================================
  Files           475      475           
  Lines         14222    14266   +44     
  Branches       1447     1452    +5     
=========================================
+ Hits          10387    10420   +33     
- Misses         2976     2987   +11     
  Partials        859      859           

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[WilliamBergamin]

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