Add a timestamp field for bans object

[Taarek]

I feel like it would be useful to know when someone was banned when you look up a specific ban or all bans in a guild. You can't use audit logs to get this info since those only last 45 days.

[Doc94]

But you dont get the time using the Snowflake id of the ban?

[z64]

Ban objects do not have their own snowflake, only a user reference and reason string.

https://discordapp.com/developers/docs/resources/guild#ban-object

[advaith1]

this would also be useful to display in the UI