feat(moderation): migrate to timeouts for mutes

[Ushie]

🐞 Issue

The bot currently uses a "Restricted" role for timing out members, which is unintended by discord and has been found to be unreliable in the following ways:

• the bot has to remove a hardcoded set of roles & this can be worked around by picking these set roles again in onboarding/roles channel [now deprecated]

❗ Solution

Migrate mutes to utilise discord's in-house Timeout feature

❓ Motivation

this will be useful to us in the following ways:

• The bot no longer has to keep track of the time passed so that it can remove the role once the time is up, that is managed by discord
• Role permissions are no longer a problem