Add Record-Level API

[nils-wisiol]

An idea how to add records to an existing RR set could be like this:

POST desec/example.com/rrsets/www/A/records/

[
"1.2.3.4",
"4.3.2.1"
]

To delete some records,

DELETE desec/example.com/rrsets/www/A/records/

[
"1.2.3.4"
]

could be used.

Some clients may have trouble with DELETE request that contain payload (but that's actually allowed).

Another issue may be that this cannot be done within a larger transaction.

[nils-wisiol]

If the RR set does not exist, minimum/default TTL could be used to create it.

Related tickets are #372, #389, #347

[peterthomassen]

Another way would be to use the record ID as an endpoint parameter. If this ID is returned during creation, it can stay in memory for thing like ACME clients, which can then conveniently delete records they no longer need.