/mute command for datapack creators and vanilla servers

As a datapack creator, I cannot implement chat moderation features 
because datapacks have no access to chat events or message filtering.

Request: Add /mute <player> [duration] and /unmute <player> commands

Why this matters:

•  Datapacks can handle /ban, /kick, but not chat moderation
•  Vanilla servers need moderation tools without plugins
•  Would complete the admin command set
•  Other games (Discord, etc.) have this as standard

Example use cases:

•  Competitive events needing chat control
•  Educational servers managing student chat
• - Family-friendly servers without plugin support