Define callbacks for on_guild_join, on_guild_remove and on_member_remove

[clement-pages]

Task description

For now, the bot does not handle the following events:

• when the bot is joining and leaving a guild
• when a member leaves a guild the bot belongs

The purpose of this issue is to add the corresponding callbacks in the SunController. A keypoint here is to properly handle the save of members and guilds data.

Validation criteria

• : Add on_guild_join callback
• : Add on_guild_remove callback
• : Add on_member_remove callback