fix istio ssl certificate name

Infrastructure Submissions:

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• [YES] Have you added an explanation of what your changes do and why you'd like us to include them? Istio SSL certificate should link to local.istio_ssl_cert_name but mis-linked to local.ssl_cert_name.
• [NO] I have updated the documentation accordingly.
• [NA] I have added tests to cover my changes.
• [YES] All new and existing tests passed.
• [YES] I have formatted the terraform code. (terraform fmt -recursive && go fmt ./...)

Current Behavior or Linked Issues

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The istio_appgateway in services_resources has configured ssl_certificate_name = local.ssl_cert_name while actual certificate is uploaded to KeyVault named istio_ssl_cert_name = "istio-appgw-ssl-cert". Gateway will not pick up the istio-appgw-ssl-cert.

Does this introduce a breaking change?

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• [NO]

MR Guildelines

• Paste TF Plan for the MR.
• Pre-Merge pipeline should be run before merging. (Azure team)
• Does the module exists for new resource.
• Is there a new variable added in the MR. (Don’t use library variables and use locals)

Other information

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