Update a function

Updates the function's mutable metadata — currently only the display name. A string sets the display name; null clears it, after which the function's name falls back to its slug. Leading and trailing whitespace is trimmed; a whitespace-only name is rejected. Acts only on a function owned by the branch: a slug that is only inherited from an ancestor branch returns 404 — rename it on the branch that owns it. Like every other change on a branch, a rename is isolated per branch: a branch forked before the rename keeps the name it had at fork time.

Note: This endpoint is currently in Private Beta.