luci-app-ddns: Helpful changes

[LecrisUT]

The current field names and settings for the ddns app are very confusing for both users and maintainers. There are issues opened about this like #2436 and various other by confused users. I would propose the following changes:

1. Allow the script maintainers to add, remove, rename, and set properties (hidden, required etc.) to fields via a .json file. For example this can look like:

{
   "name": "My new DDNS script",
   "fields": [ {
      "name": "record name",
      "required": true
   }, {
      "name": "domain",
      "required": true
   }]
}

2. For ddns-scripts, provide a complete example curl script including any possible error catchers. There are some issues out there linked to an incomplete ddns-script. This could also be used to add better tests for the CI.
3. Add a view log option outside the edit dialog, and output any or all the contents in the \var\log, DATFILE, ERRFILE.
4. Lowest priority, but would definitely be appreciated: Provide a contact method for when any of the scripts are failing.

Situations where this is helpful:

• Remove the confusion when you have to input the record name into the username field.
• Allow ddns on local servers like PowerDNS
• Simplify and clarify scripts, e.g. remove the need for param_opt

I understand that this could break some of the current ddns-scripts, however some of them could use a rewrite to better manage error at the very least.

[feckert]

I agree with you completely. That's why I changed the database to json. Before, it was a file with which you added or deleted something with SED. If you want, you can create a proof of concept how you imagine it, then I can look at it in the code.

[adelton]

I now filed #7559 to actually show the Update URL. It is not the general customization suggested here but given this issue did not get addressed so far, maybe being able to see the URL in the UI with the placeholders might help a bit?