fix SRV and MX records

[Adphi]

SRV records are now working using a canonical value e.g. "10 10 993 mail.example.org"
MX records are now also working using both canonical value e.g. "10 example.org" or by setting the Priority field and a simple value e.g. "example.org"
The search records now remove the zone from the name before setting it to the fqdn form

It also adds some basic tests (#3) for usual mail server records (A, MX, TXT, SRV) and CNAME.

[mholt]

Thanks for the PR! I like where this is going.

As mentioned in my comment, maybe we should get rid of Priority and Weight and other specialized fields and have helpers instead (kind of like we do for SRV, but with the fixes obviously).

[Adphi]

Sorry, I did not had enough time this week to come back to you.
I expect to find some time in the following ones to start working on the following points:

• PR on the main repo to remove the record's extra fields
• PR on the main repo to add methods for target conversion to individual record types (there is a high probability that this one will use the miekg implementation)
• We need to settle the destination structs types from the previous point
• update this PR to use theses methods
• back to the main repo, write some minimal/draft conformance tests
• implement them here as draft guidelines

[balki]

I needed to create MX record. Had to add the patch below:
https://gitea.balki.me/balki/cloudflare-dns-cli/commit/581d6613cc87b1c469f40c6456d83614f53c7b2e

[mholt]

@balki Thank you!

@Adphi Any chance you'd have interest/time to finish up this one?