Add support for CNAME record type for subdomains

[manedurphy]

This change allows the user to configure subdomains as CNAME records which point to the base domain.

Sample configuration:

"subdomains": [
    {
        "name": "@"
    },
    {
        "name": "sub1",
        "type": "cname"
    },
    {
        "name": "sub2",
        "type": "cname"
    }
]

• The base domain might be my-domain.com, which has an A record
• Both the sub1.my-domain.com and sub2.my-domain.com subdomains will have a CNAME record which point to my-domain.com