Add Discord player logging to notify when players join and leave the server

[xHyperElectric]

Context

Add discord player logging to notify via Discord webhook when players join and leave the server.

Adds this feature mentioned in #324

Script for notifying the public join/leave channel and broadcasting via RCON when a player joins or leaves:

Choices

I only 1 line for joining and one line for leaving inside the pre-existing player_logging.sh loops that are currently used for broadcasting to the server. I added lines to call the pre-existing function DiscordMessage() to send a message in the loop.

I added two env variables to allow the ability to change the join and leave messages. (DISCORD_PLAYER_LEAVE_MESSAGE and DISCORD_PLAYER_JOIN_MESSAGE)

I'm quite new to docker so I could be wrong, but I believe the way I did it would work. In the dockerfile I left ${player_name} in both messages for them to be substituted later. If I understand correctly, the string "${player_name}" can not be removed if the message is changed, otherwise the substitution would fail.

I did not add anything in the message to indicate how long a player was on the server before they left.

Test instructions

I am unable to test it myself, therefore I haven't.

1.) Create a DISCORD_WEBHOOK_URL
2.) Have a player join or leave the server
3.) Check for a message in the channel for which the DISCORD_WEBHOOK_URL is set up to post to

Checklist before requesting a review

• I have performed a self-review of my code
• I've added documentation about this change to the README.
• I've not introduced breaking changes.

[xHyperElectric]

I'm not familiar with docusaurus but it seems the check failed because I didn't properly escape the ${player_name} in the docusaurus docs.

Error: Docusaurus server-side rendering could not render static page with path /getting-started/configuration/server-settings because of error: player_name is not defined