UpdateTeamStackPermissions

Modifies the permissions that a specific team has for the referenced stack. This allows setting the team's permission level (read, write, admin) for a single stack without affecting the team's permissions on other stacks. The team does not need an existing grant on the stack; one is created if it is missing. Returns 400 if the permission level is invalid. Returns 403 if the caller lacks permission to update the team. Returns 404 if the team does not exist.