luci-app-acme: render DNS API fields from the Structured Info

luci-app-acme: render DNS API fields from the Structured Info

The ACME.sh DNS API scripts have a description of their options.
Now we can parse them and render all necessary fields for a specific DNS API.
When a user changes the DNS API specific options, their value is copied into the Credentials list, thus keeping backward compatibility.
Some DNS APIs like CloudFlare or Selectel have alternative options (usually API v2).
To see the Alternative credentials, a user should click on the Alt Options flag.

Signed-off-by: Sergey Ponomarev <redacted>