Add sandbox attribute to the iframe

[kopecmi8]

Based on https://community.powerbi.com/t5/Service/Power-BI-Embedded-iframe-sandbox-attribute/m-p/2362079

We want to add sandbox attribute for safe embedding of your reports in our application. I tried to find another way, but the library currently doesn't allow us to pass the attribute in any way.

[Duskfen]

@mattmazzola kindly asking, why does this not get merged

[aliabufoul]

I agree with adding the sandbox attribute in general.
The current changes might be risky as it can potentially block some of the capabilities for embedded reports.
For example, if allows-download is not added to the sandbox attribute, it might block the capability of exporting visual data.
We prefer to do this change internally, so we can test it against the capabilities of embed