fix(apig/ssl_certificates): fix some issues

[946596029]

What this PR does / why we need it:
fix(apig/ssl_certificates): fix some issues

Which issue this PR fixes:
change resource name to huaweicloud_apig_instance_associated_ssl_certificates

Special notes for your reviewer:

Release note:

PR Checklist

• Tests added/passed.

Prepare to calculate the coverage the following command:
TF_ACC=1 go test "./huaweicloud/services/acceptance/apig" -v -coverprofile="./huaweicloud/services/acceptance/apig/apig_coverage.cov" -coverpkg="./huaweicloud/services/apig" -run TestAccDataSourceInstanceAssociatedSSLCertificates_basic -timeout 360m -parallel 10
=== RUN   TestAccDataSourceInstanceAssociatedSSLCertificates_basic
=== PAUSE TestAccDataSourceInstanceAssociatedSSLCertificates_basic
=== CONT  TestAccDataSourceInstanceAssociatedSSLCertificates_basic
    acceptance.go:955: Before running APIG acceptance tests, please ensure the env 'HW_APIG_DEDICATED_INSTANCE_ID' has been configured
--- SKIP: TestAccDataSourceInstanceAssociatedSSLCertificates_basic (0.00s)
PASS
coverage: 1.4% of statements in ./huaweicloud/services/apig
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/apig      0.124s  coverage: 1.4% of statements in ./huaweicloud/services/apig

• Documentation updated.
• Schema updated.
• CheckDeleted.