[BUG] Container Instance cannot update due to secure value env

[ChenTanyi]

Describe the bug
This is the service problem. When updating the container instance, if there is secure value in any container environment, it could only be updated successfully for setting a new secure value or deleting the secure environment.

Code Snippet
example:

• create a container

{
    "name": "nginx",
    "properties": {
        "image": "nginx",
        "ports": [
            {
                "protocol": "TCP",
                "port": 80
            }
        ],
        "environmentVariables": [
            {
                "name": "env",
                "secureValue": "val"
            }
        ],
        "resources": {
            "requests": {
                "memoryInGB": 1.5,
                "cpu": 1.0
            }
        }
    }
}

• return json

{
    "name": "nginx",
    "properties": {
        "image": "nginx",
        "ports": [
            {
                "protocol": "TCP",
                "port": 80
            }
        ],
        "environmentVariables": [
            {
                "name": "env"
            }
        ],
        "resources": {
            "requests": {
                "memoryInGB": 1.5,
                "cpu": 1.0
            }
        }
    }
}

• for updating:
  • If I use original return json, it would throw the cloud exception about:

  The environment variable 'env' in container 'nginx' of container group 'cgtest' is invalid. One and only one property of 'value' and 'secureValue' can be specified in an environment variable.
  

  • If I delete the 'environmentVariables' parameter, it would return with empty environment for nginx, but actually I need the environment.
  • Only if I set the secureValue with same value (or a new value), I can update other parameters.

Expected behavior
I can send with the following 'environmentVariables' to update other parameters for container instance.

"environmentVariables": [
    {
        "name": "env"
    }
]

For Example
I send the following json and it could update cpu and memory, while the environments stay same as it would be.

{
    "name": "nginx",
    "properties": {
        "image": "nginx",
        "ports": [
            {
                "protocol": "TCP",
                "port": 80
            }
        ],
        "environmentVariables": [
            {
                "name": "env"
            }
        ],
        "resources": {
            "requests": {
                "memoryInGB": 2.0,
                "cpu": 2.0
            }
        }
    }
}

Information Checklist
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[ChenTanyi]

Blocking PR :
#766
Azure/azure-libraries-for-net#714

[ChenTanyi]

It is said that the issue may be solved in the next api-version