Add Klipper, OctoPrint and PrusaLink printers from the API

POST /farms/:id/printers now takes any of the four vendors the gateway can
drive. Credentials depend on the vendor: Bambu needs an access code and
serial, OctoPrint and PrusaLink an API key, Klipper nothing. A missing one
is a 422 naming what is needed. The API key is relayed to the gateway and
kept out of logs and errors like the access code.

The printer_vendor enum gains octoprint (migration 0006); PrusaLink is
stored as prusa, the name the enum already had.

scripts/e2e-vendors.sh adds each kind through the API against a fake REST
printer (scripts/fake-http-printer.ts) and runs a job through the real
scheduler to completion. The fake shares its author's reading of the docs
with the driver, so this proves the plumbing, not the protocols.

drizzle/0006_octoprint_vendor.sql

@@ -0,0 +1 @@
+ALTER TYPE "printer_vendor" ADD VALUE 'octoprint';