Extend Host User Creation to support a static set of users

[rosstimothy]

What would you like Teleport to do?

Support creating out of band users with pre-set UID, GID and sudo entitlements.

What problem does this solve?

Host user creation is lazy and only creates users at time of login. There are some use cases which require that a static set of predefined users always exist.

[rosstimothy]

• Add proto Add static host user proto defs #44610
• Implement backend storage service Add static host user service #44778
• Implement gRPC service Static host users - Add gRPC service #45292
• Add resource to cache Add static host user cache #45573
• Implement tctl support Add static host user tctl #46093
• Watch for and apply users in the agent Apply static host users to nodes #46365
• Add audit events Add audit events for static host users #46246
• Add test coverage for lib/srv.StaticHostUserHandler Add static host user tests #47051
• Documentation Add static host user docs #46650
• Add Terraform Provider support Add static host users to Terraform provider #46826
• Update RFD Update static host user RFD #47066

[rosstimothy]

Test Plan

• Creating user from resource
  • login doesn't exist on host -> create the user
  • login exists on host, not managed by Teleport -> do nothing
  • login exists on host, insecure-drop -> do nothing
  • login exists on host, keep -> do nothing
• More than one matcher in an SHU matches a node -> log a warning and do nothing
• Deleting SHU resource doesn't remove the user/home directory/sudo entitlements
• Automatic Host User Creation
  • keep mode doesn't update/overwrite a static user
  • drop mode doesn't update/overwrite/delete a static user