Add Jakarta EE compatible Socket Mode client ref: #919

This pull request adds two new optional modules:

slack-jakarta-socket-mode-client
bolt-jakarta-socket-mode

The currently available Socket Mode client's default implementation uses tyrus-standalone-client 1.x, which is compatible with javax.websocket-api APIs. The Jakarta EE version of this interface is the jakarta.websocket-client-api APIs, and tyrus-standalone-client 2.x is compatible with it. Since it's not feasible to have both tyrus-standalone-client 1.x and 2.x in the same module's dependencies, I have added a new module named slack-jakarta-socket-mode-client. See https://github.com/slackapi/java-slack-sdk/issues/919 for more details.

Developers can initialize the Jakarta-compatible SocketModeClient this way:

import com.slack.api.Slack;
import com.slack.api.jakarta_socket_mode.JakartaSocketModeClientFactory;

public class Example {
  public static void main(String[] args) throws Exception {
    var appToken = System.getenv("SLACK_APP_TOKEN");
    var slack = Slack.getInstance();
    // Java EE compatible Socket Mode client
    slack.socketMode(appToken).connect();
    // Jakarta EE compatible Socket Mode client
    JakartaSocketModeClientFactory.create(slack, appToken).connect();
  }
}

In the same way, I’ve added a new Jakarta-compatible module, which is equivalent to bolt-socket-mode. Here is the demo code. As you can see, just replace the dependency and imports in the code:

import com.slack.api.bolt.App;
import com.slack.api.bolt.jakarta_socket_mode.SocketModeApp;

public class Example {
  public static void main(String[] args) throws Exception {
    var app = new App();
    app.command("/hi", (req, ctx) -> {
      ctx.say("Hi there!");
      return ctx.ack();
    });
    var appToken = System.getenv("SLACK_APP_TOKEN");
    // Switch from com.slack.api.bolt.socket_mode to com.slack.api.bolt.jakarta_socket_mode
    new SocketModeApp(appToken, app).start();
  }
}

The reason behind this enhancement is that many Java-focused companies are planning to eliminate the legacy javax.* dependencies from their project settings. I don't think the short-term risk of having a javax.websocket dependency is significant, but it seems it's about time to provide an option for migration on the developers' side.

Category (place an `x` in each of the `[ ]`)

[ ] bolt (Bolt for Java)
[x] bolt-{sub modules} (Bolt for Java - optional modules)
[ ] slack-api-client (Slack API Clients)
[ ] slack-api-model (Slack API Data Models)
[ ] *slack-api--kotlin-extension** (Kotlin Extensions for Slack API Clients)
[x] slack-app-backend (The primitive layer of Bolt for Java)

Requirements

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Codecov Report

Attention: Patch coverage is 68.43854% with 95 lines in your changes missing coverage. Please review.

Project coverage is 74.82%. Comparing base (e542f29) to head (a76768d). Report is 1 commits behind head on main.

Files	Patch %	Lines
...et_mode/impl/JakartaSocketModeClientTyrusImpl.java	71.09%	39 Missing and 11 partials :warning:
...ck/api/bolt/jakarta_socket_mode/SocketModeApp.java	62.50%	28 Missing and 5 partials :warning:
...ta_socket_mode/JakartaSocketModeClientFactory.java	25.00%	11 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1352 +/- ## ============================================ - Coverage 74.99% 74.82% -0.18% - Complexity 4203 4274 +71 ============================================ Files 453 457 +4 Lines 12975 13276 +301 Branches 1342 1369 +27 ============================================ + Hits 9731 9934 +203 - Misses 2462 2544 +82 - Partials 782 798 +16 ```

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slackapi / java-slack-sdk