Fix custom domain verification example in documentation

[hozzer]

🔧 Changes

The documentation for the auth0_custom_domain_verification resource references the wrong value in the name field in the digitalocean_record resource block example:

resource "auth0_custom_domain" "my_custom_domain" {
  domain = "login.example.com"
  type   = "auth0_managed_certs"
}

...

resource "digitalocean_record" "my_domain_name_record" {
  domain = "example.com"
  type   = upper(auth0_custom_domain.my_custom_domain.verification[0].methods[0].name)
  name   = "${auth0_custom_domain.my_custom_domain.domain}." # Incorrect reference to "login.example.com"
  value  = "${auth0_custom_domain.my_custom_domain.verification[0].methods[0].record}."
}

This would create the following record for the example.com domain:

Record Name	Type	Value
login.example.com.	TXT	"SOME_UUID_V4"

which incorrectly constructs the record as login.example.com.example.com

Instead, we want:

Record Name	Type	Value
_cf-custom-hostname.login	TXT	"SOME_UUID_V4"

which correct constructs the intended DNS record as _cf-custom-hostname.login.example.com

An example auth0_custom_domain.my_custom_domain.verification[0].methods would look like this:

"methods" = tolist([
  tomap({
    "domain" = "_cf-custom-hostname.login.example.com"
    "name" = "TXT"
    "record" = "SOME_UUID_V4"
  })
])

So we should make use of auth0_custom_domain.my_custom_domain.verification[0].methods[0].domain instead. Note we also need to remove the .example.com suffix.