feat(import_transform): skip records with import_transform_skip set

[tlimoncelli]

Problem:

• IMPORT_TRANSFORM/IMPORT_TRANSFORM_STRIP need to be able to skip certain records.

Solution:

• With this PR, if the metadata for a record includes "import_transform_skip" (any value), that record is skipped

[tlimoncelli]

@costasd Hi Costas! It looks like NS1 has finally disabled URLFWD: https://github.com/StackExchange/dnscontrol/actions/runs/11731300660/job/32681410264

[costasd]

@tlimoncelli ah nice, will prepare a PR to remove it completely.