Add Private Messaging

[beanbeanjuice]

Pull Request

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Description

Added private messaging and their subsequent commands. You can also set .

Fixes #164

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Type of Change

• [ ] Bug Fix (Small Non-Code Breaking Issue)
• [ ] Bug Fix (Critical Code Breaking Issue)
• [x] Feature (Something New Added to the Code)
• [ ] Improvement (Improving An Existing Section of Code)
• [ ] Documentation Update
• [ ] Security Vulnerability

Changes

• [x] Internal Code
• [x] Documentation
• [ ] Other: _____

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Test Configuration

• Hardware:
  • CPU: AMD Ryzen 7 5800x3D
  • GPU: Nvidia RTX 3080
  • RAM: 32 GB DDR4
• JDK: Java OpenJDK 17

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Checklist

• [x] This pull request has been linked to the appropriate issue on GitHub. (Use the development section on the right.)
• [x] The code follows the style guidelines.
• [x] A self-review of the code was performed on GitHub.
• [x] Appropriate comments and javadocs were added in your code.
• [x] Appropriate changes have been made to the documentation.
• [x] Appropriate changes have been made to the README.md file.
• [x] No warnings are produced when the code is run.
• [x] Appropriate tests exist for this pull request.
• [x] New and existing Maven CI tests have passed.
• [x] The pull request is properly merging into the correct branch.
• [x] All existing local code has been pushed to the GitHub repository.
• [x] Changes have been documented in the current draft ProxyChat Releases update.