[Network] Fix #21716: az network private-dns zone import: Allow hyphenated SRV records

[huws]

Description
This is necessary to allow hyphenated SRV records targets to be successfully imported. Today, such imports fail, as described in #21716

Testing Guide
Without the fix, importing this valid zone file (db.example.com) will fail:

@                 3600 IN SOA  ns admin ( 2014010800 ; Serial
                                          3600       ; Refresh
                                          3600       ; Retry
                                          3600       ; Expire
                                          300 )      ; Minimum TTL

_sip._tcp.pool 300 IN SRV 20 10 5060 valid-target-1
_sip._tcp.pool 300 IN SRV 20 10 5060 valid-target-2
_sip._tcp.pool 300 IN SRV 20 10 5060 valid-target-3

Failure output from import using az network private-dns zone import --resource-group <RG NAME> --name example.com --file-name db.example.com:

== BEGINNING ZONE IMPORT: example.com ==
	
	(1/4) Imported 1 records of type 'soa' and name '@'
	(BadRequest) The list of record sets of type 'SRV' may not contain multiple entries with the same '(priority, weight, target)'.
	Code: BadRequest
	Message: The list of record sets of type 'SRV' may not contain multiple entries with the same '(priority, weight, target)'.
	
	== 1/4 RECORDS IMPORTED SUCCESSFULLY: 'example.com' ==

With the fix, this import succeeds with the output:

	== BEGINNING ZONE IMPORT: example.com ==
	
	(1/4) Imported 1 records of type 'soa' and name '@'
	(4/4) Imported 3 records of type 'srv' and name '_sip._tcp.pool'
	
	== 4/4 RECORDS IMPORTED SUCCESSFULLY: 'example.com' ==

History Notes

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[yonzhan]

Network

[necusjz]

@huws Overall LGTM, but please refine the PR title and rebase with the latest changes from dev branch.

[necusjz]

@huws, I was aware that this PR introduced too many others' commits, i.e., too many unrelated file changes. So, please make it clean and only introduce related changes. Thanks.

[huws]

Apologies - not sure what happened, there. The PR is now clean - just my one commit.

[necusjz]

@huws never mind, our CI was also down at that moment.

[necusjz]

/azp run

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