Pinterest Block: add board size options

[jeherve]

We may add a size option to the block sidebar, since Pinterest apparently allows you to set a data-pin-width attribute to control the size of the embed.

I could also imagine some folks wanting to show more of their board instead of the first 700px of it or so, but I am not sure that's an option offered by Pinterest.

[stale]

This issue has been marked as stale. This happened because:

• It has been inactive in the past 6 months.
• It hasn’t been labeled `[Pri] Blocker`, `[Pri] High`.

No further action is needed. But it's worth checking if this ticket has clear reproduction steps and it is still reproducible. Feel free to close this issue if you think it's not valid anymore — if you do, please add a brief explanation.