feat(infoblox): add AAAA (IPv6) record support

[MaxRink]

Closes #37.

What

Adds AAAA (IPv6) records end-to-end, following the existing patterns for A records.

• ToAAAAResponseMap() maps []ibclient.RecordAAAA onto the shared ResponseMap using the ibclient.AaaaRecord type constant.
• Records() fetches record:aaaa per zone through PagingGetObject, the same way A records are fetched (same View/Ea/Zone handling, isNotFoundError tolerance and FailedApiCallsTotal accounting).
• ToHostAAAAResponseMap() surfaces the Ipv6Addrs of host records as AAAA endpoints, mirroring how Ipv4Addrs already become A endpoints. Both host mappers now skip records carrying no address of the respective family, so an IPv4-only or IPv6-only host record no longer yields an endpoint with an empty target.
• recordSet() builds a RecordAAAA for create/update/delete, looking the existing object up by name + ipv6addr.
• getRefID() resolves the object reference and log fields for RecordAAAA.

Infoblox can return the same IPv6 address more than once for a name (the same address in a different but equivalent notation). Left alone that produces a permanently dirty plan, so ToAAAAResponseMap de-duplicates targets via a new ResponseDetails.Contains helper.

Why

The provider handled A, CNAME, TXT, NS, host and PTR records only. Two consequences today:

1. AAAA records already present in a zone are invisible to Records().
2. Any AAAA endpoint in a plan is silently dropped by recordSet() — the switch ep.RecordType has no matching case, so it returns a zero value with err == nil. No error surfaces; the record simply never gets created.

So IPv6 services managed through ExternalDNS could not be reconciled against Infoblox at all.

Not included

PTR records are still created for A records only. The reverse-zone path is IPv4-oriented (rfc2317.CidrToInAddr, net.ParseCIDR + Contains, and record:ptr keyed on ipv4addr); ip6.arpa nibble-zone delegation needs separate handling and is better as its own change. Getting it half-right would create broken reverse records.

Testing

internal/infoblox/infoblox_test.go extends the existing mock connector (create/get/delete/update cases, the paging response type, object factories, plus a new host-record factory taking IPv4 and IPv6 address lists) and covers:

• fetching AAAA records, including the record:aaaa GetObject request and query params, in both the plain and view variants
• multi-target AAAA and duplicate-target de-duplication
• dual-stack and IPv6-only host records
• create / update / delete through ApplyChanges, including in-filter and out-of-filter domains and the reverse/PTR variant

go build, go vet, go test ./... and golangci-lint run ./... (0 issues) all pass; main was verified green beforehand so nothing pre-existing is attributed here.

The new tests were mutation-checked to confirm they actually assert the new behaviour: removing the AAAA fetch, the de-duplication guard, or the recordSet AAAA case each makes them fail.

Also adds AAAA to the supported-records table in the README.

Context

We maintain a fork of external-dns carrying an equivalent AAAA patch against the old in-tree Infoblox provider (removed upstream in v0.15.0). Contributing it here instead lets us drop that fork and consume stock upstream external-dns — which is why the implementation deliberately follows this repo's conventions rather than porting the old provider's shape.