Add custom error handler support to Socket Mode adapter

[seratch]

ref: https://github.com/slack-samples/bolt-java-starter-template/issues/199

This pull request adds custom error handler support to SocketModeApp, which is a built-in Socket Mode adapter. I've checked other adapters too but I don't see the necessity to add similar to others so far.

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)
• [ ] slack-app-backend (The primitive layer of Bolt for Java)

Requirements

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[codecov[bot]]

Codecov Report

Merging #1232 (883d69f) into main (37d738c) will decrease coverage by 0.78%. Report is 51 commits behind head on main. The diff coverage is 83.33%.

@@             Coverage Diff              @@
##               main    #1232      +/-   ##
============================================
- Coverage     74.87%   74.09%   -0.78%     
- Complexity     4074     4085      +11     
============================================
  Files           436      440       +4     
  Lines         12835    12995     +160     
  Branches       1301     1310       +9     
============================================
+ Hits           9610     9629      +19     
- Misses         2464     2598     +134     
- Partials        761      768       +7     

Files	Coverage Δ
.../com/slack/api/bolt/socket_mode/SocketModeApp.java	72.82% <83.33%> (+0.67%)	:arrow_up:

... and 24 files with indirect coverage changes

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