[Release] Update index.json for extension [ aks-preview ]

[azclibot]

[Release] Update index.json for extension [ aks-preview ]

Triggered by Azure CLI Extensions Release Pipeline - ADO_BUILD_ID=521364

Last commit against master: 745bbb3

[azuresdkci]

If this PR is for a new extension or change to an existing extension, use the following to try out the changes in this PR:

docker run -it microsoft/azure-cli:latest
export EXT=<NAME>
pip install --upgrade --target ~/.azure/cliextensions/$EXT "git+https://github.com/azclibot/azure-cli-extensions.git@release-20200903-050129#subdirectory=src/$EXT&egg=$EXT"