feat: adds support for MX and TXT records

[phenax]

Fixes #844

• Add and test MX
• Add and test TXT
• Add proper validation for CNAME and restrict usage with MX records
• Add restricted list of domain names
• Update docs
• Update maintainer docs

[quackduck]

Whoa, fantastic!

[phenax]

Added MX and TXT record support. Currently working on an issue and testing out different variants. Will update the docs soon.

Design choices made in this PR

• Only 1 TXT record can be specified here even though the standard allows multiple TXT records. This is for simplicity and can be changed in the future if needed.
• MX records will have priority set automatically based on the order specified in the record file.
  Example:

{
  "record": {
    "MX": [
      "mx1.example.com",
      "mx2.example.com",
    ]
  }
}

Here, mx1.example.com will have priority 20 and mx2.example.com will have priority 21 and so on.

Known limitations / restrictions

• The same review rules that apply to CNAME, apply to MX records. TXT records however can be any string.
• MX cannot be used with a CNAME record, the user will have to create another record for their emails. This is a limitation in DNS itself. As an alternative, we can ask them to use A records instead (for github pages users)
• Will be adding a few restrictions on subdomain names (Eg: support, help, etc) that will be in the tests

@is-a-dev/maintainers, Let me know if there's any changes needed.

[github-actions]

The changes have been published!! It should reflect in less than 24 hours.

Here's what you need to do next

If your domain points to a server you own, add domain-name.is-a.dev to your server config. For https, you will have to configure ssl certificate to allow the new subdomain.

For github pages users,

• Go to your github page repo (user/user.github.io)
• Open up the settings tab
• Scroll down to the Github pages section
• In the Custom domain text input, enter the domain you registered (domain-name.is-a.dev)
• Check the Enforce HTTPS checkbox below the input
• Give it some time to reflect and you should be good to go

Need help with your domain?

If you are having trouble setting up your domain, create an issue. I will try my best to get back to you asap!

Made a mistake in the record?

Don't worry, you can create a new pull request with the corrections

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