refactor(apig/sign): support refresh functions for associate resource

[Lance52259]

What this PR does / why we need it:
Support the refresh functions for the signature associate resource.

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

Special notes for your reviewer:

Release note:

1. support refresh functions for associate resource

PR Checklist

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

Acceptance Steps Performed

make testacc TEST='./huaweicloud/services/acceptance/apig' TESTARGS='-run=TestAccSignatureAssociate_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/apig -v -run=TestAccSignatureAssociate_basic -timeout 360m -parallel 4
=== RUN   TestAccSignatureAssociate_basic
=== PAUSE TestAccSignatureAssociate_basic
=== CONT  TestAccSignatureAssociate_basic
--- PASS: TestAccSignatureAssociate_basic (722.11s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/apig      722.154s

[github-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This PR has been approved by: @Lance52259

[jinyangyang222]

/lgtm