Add myaddr dynamic dns provider

[brianshea2]

Adds new dynamic dns provider: https://myaddr.tools
Partially fixes #728 (additional PR for public IP provider to come)
Cheers!

[qdm12]

Thanks for the PR 🎖️ 💯 !

A few comments of things to change here and there, but before jumping in this: would you mind creating another separate pull request for the public ip feature, since it should be a separate commit/PR really. Thank you 🙏 👍

[brianshea2]

Thank you for the quick review :) I believe I've addressed all your comments and made the code more consistent with the project.

I've reverted the public IP provider addition for now and will open a separate PR for that.

I understand your want for providing the "domain" to be consistent with other providers, and have removed the initialization code which fetched the domain corresponding to the provided "key". My concern now is there's nothing explicitly linking the provided "key" and "domain". I believe I've described the "domain" adequately in docs/myaddr.md to this point. But to reiterate, the provided "key" is the only identifier sent to the provider api, and is used to update all [*.]name-corresponding-to-key.myaddr.{tools,dev,io} in one fell swoop, which may or may not agree with the separately-user-provided "domain", now used only for checking if an update is required. What are your thoughts here? It's possible to perform an additional api request during each update to fetch the domain corresponding to "key" and compare to the provided "domain" if wanted.

[qdm12]

I believe I've addressed all your comments and made the code more consistent with the project.

Awesome 💯

I've reverted the public IP provider addition for now and will open a separate PR for that.

Perfect 🥇

It's possible to perform an additional api request during each update to fetch the domain corresponding to "key" and compare to the provided "domain" if wanted.

Eh it's a bit on the user if he/she sets a key not matching the domain. We can do foolproof checks as much as possible, but this seems like a bit too much at the cost of over-complicating it 😄 The API will probably just say the key is wrong anyway.

I did however add a little check to prevent multiple domains to be defined in a myaddr settings block since one key is for one domain (and its subdomains), so there would be no point handling it as different entries/updates in parallel, except getting banned for sending too many update requests 😄

Merging this !!