Fixes #18398: Use consistent DNS parameter naming

[ekohl]

• fqdn is what is defined in the API and should only be in dns_api.rb
• value is what is defined in the API and should only be in dns_api.rb
• name is the DNS name you query for
• content is the result your DNS server should return

This should avoid confusion with types where the content is also a valid
hostname so fqdn is ambigious.

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[dmitri-d]

I think that in most places these changes made method signatures more confusing: def create_a_record(fqdn, ip) is much clearer about its parameter expectations compared to def create_a_record(name, content).

Perhaps instead of trying to come up with a common parameter naming convention we should rename parameters in cname-related method to more descriptive ones? For example: def create_cname_record(existing_fqdn, new_alias)?

[ekohl]

I agree with it on create_a_record that it's less readable, but my reasoning is that I want the Record class to be much closer to actual DNS. I'll first try to get other refactorings (like #511) in and then circle back here.