Add custom field support in IPAM Prefix

[nothinux]

Add custom field support in IPAM Prefix

TEST_FUNC=TestAccNetboxPrefix_basic make testacc-specific-test
⌛ Startup acceptance tests on http://localhost:8001 with version v3.7.1
⌛ Testing function TestAccNetboxPrefix_basic
TF_ACC=1 go test -timeout 20m -v -cover netbox/*.go -run TestAccNetboxPrefix_basic
=== RUN   TestAccNetboxPrefix_basic
=== PAUSE TestAccNetboxPrefix_basic
=== CONT  TestAccNetboxPrefix_basic
--- PASS: TestAccNetboxPrefix_basic (13.82s)
PASS
coverage: 9.0% of statements
ok      command-line-arguments  15.227s coverage: 9.0% of statements

[fbreckle]

LGTM but can you please run make docs to regenerate the docs?

[nothinux]

done @fbreckle