[Feature][Docs] Nat gateway support querying by enterprise_project_id

[Lance52259]

What this PR does / why we need it:
Enterprise project id is supported with Nat gateway support, but it can not be used to querying gateway list.

Which issue this PR fixes:
(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

NONE

Special notes for your reviewer:

Release note:

1. add enterprise project id to Nat gateway datasource.
2. fixed client exception call (natV2Client).
3. update acc test with enterprise project id.

PR Checklist

• Tests added/passed.
• Documentation updated.
• Schema updated.

Acceptance Steps Performed

make testacc TEST='./huaweicloud' TESTARGS='-run=TestAccNatGatewayDataSource_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run=TestAccNatGatewayDataSource_basic -timeout 360m -parallel 4
=== RUN   TestAccNatGatewayDataSource_basic
=== PAUSE TestAccNatGatewayDataSource_basic
=== CONT  TestAccNatGatewayDataSource_basic
--- PASS: TestAccNatGatewayDataSource_basic (85.88s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       85.928s