expose iframe.html.ejs to user via config object.

[klh]

instead of the whole preview-head.html thing just expose the complete iframe.html.ejs template via the config object.

usage scenarios:

• for instance, adding lang="myLanguage" to the Html tag (impossible to do with the current solution.)

it would just make life easier for most people.

[stale]

Hi everyone! Seems like there hasn't been much going on in this issue lately. If there are still questions, comments, or bugs, please feel free to continue the discussion. Unfortunately, we don't have time to get to every issue. We are always open to contributions so please send us a pull request if you would like to help. Inactive issues will be closed after 60 days. Thanks!

[stale]

Hey there, it's me again! I am going close this issue to help our maintainers focus on the current development roadmap instead. If the issue mentioned is still a concern, please open a new ticket and mention this old one. Cheers and thanks for using Storybook!