Allow embedding of deno deploy playground

[ayame113]

deno deploy playground is a code sharing service like code-pen.
https://deno.com/blog/deploy-beta3#playgrounds

We can embed code by allowing code that contains an iframe tag like the one below. (We can get this code from https://embed.deno.com/?id=my-server-example&layout=both.)

<iframe width="100%" height="600" src="https://embed.deno.com/playground/my-server-example?layout=both"></iframe>

It would be great if qiita could embed a deno deploy playground.

[kyntk]

@ayame113 Thank you for creating issue.
We are planning to enable embedding of other notations as well, so we will consider this as well at that time.

[ayame113]

@ayame113 Thank you for creating issue.
We are planning to enable embedding of other notations as well, so we will consider this as well at that time.

Thanks!