feat: configurable join/leave recipients (exclude-self, exclude-server)

[realdody]

Pull Request

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Description

Adds config options to exclude sending join/leave messages to self (player that joins/leaves), server (every player on the same server as the player, but doesn't exclude the player), and both (every player on the same server)

Added recipients.exclude-self and recipients.exclude-server for join/leave.
Aligned behaviour across Velocity and Bungee.
Added documentation to README.md and plugin config.

Closes #251

Related PRs: N/A

Prerequisites: N/A

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Checklist

• The code follows the style guidelines.
• A self-review of the code was performed on GitHub.
• Appropriate comments and javadocs were added in your code.
• Appropriate changes have been made to the documentation.
• Appropriate changes have been made to the README.md file.
• Appropriate tests exist for this pull request.