Machine ID: tctl support for modifying Bots roleset

[strideynet]

Currently our guides are a little awkward since you need to know the roles a bot will have at the time of its creation.

It'd probably be beneficial to have a easy command for this.

I'm easy on the UX but I think something like the following would work:

tctl bots update bot-name --add-role role-name
tctl bots update bot-name --set-roles role-name,role-name-2

I'd recommend this work comes after #33808 otherwise this will need to be redone.

[strideynet]

It'd be beneficial to follow this up with updating the documentation to use this.

Ensure we also add this to the CLI Reference for tctl.