Provide a way to manage Teleport join tokens via web UI

[webvictim]

What would you like Teleport to do?

Provide a way to manage Teleport join tokens via web UI. See currently active tokens, the services they allow, their expiry time, add new ones, delete old ones, etc.

What problem does this solve?

With the newer Teleport Discover wizards, most people are using automatically generated tokens that are completely abstracted away from them. When they want to add another service to their running agent, they suddenly get plunged into a world of hurt needing to log in and use tctl remotely which is an unfamiliar environment for them.

If a workaround exists, please include it.

Use tctl and ask support for help.

Task breakdown:

• [ ] Add sort cache service for JoinTokens
• [ ] Add grpc methods/pagination for ListJoinTokens
• [ ] Create apiserver routes for JoinTokens CRUD
• [ ] UI/UX for the web component (prototype done by @avatus , feedback from kenny after)
• [ ] Final updates/adjustments to web UI
• [ ] Integrate with Discover UI (token reuse)

[webvictim]

(I couldn't find a duplicate issue for this if one exists, sorry)