dns/ddnsclient: add TransIP support

[mgroenhoff]

I have been using an older version of this code for quite some time now and finally found the time to polish and submit it.

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• I opened an issue first for non-trivial changes and linked it below.
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Related issue
No issue (yet)

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Describe the problem
While the acme client has TransIP support, ddnsclient has not (yet)

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Describe the proposed solution
Add ddnsclient service for TransIP

API Docs: https://api.transip.nl/rest/docs.html#header-authentication

Relevant Account Settings:

• Username: your TransIP username
• Password: Generate a new key-pair at the control panel and paste the private key in PEM format in this field (Make sure to disable the IP filter flag. Because DynDNS)
• Zone: One of the domain names listen in the control panel
• Hostname(s): The DNS entry record names to update. For example: "@,*"
• TTL: Speaks for itself

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[mgroenhoff]

How do I request a review? Do I need to create an issue first?